OLED is a new display technology, used to create thin, power efficient and bright displays. Today OLEDs are used in mobile phones, tablets, digital cameras and even TV sets - as OLEDs are considered the best display technology ever.
Apple's OLED iPhone
Apple's 10th anniversary iPhone X is the company's first OLED Phone - with a 5.8" 1125x2436 (458 PPI) flexible Super AMOLED display that covers almost the entire front of the phone, HDR, dual lens camera, a Hexa-core A11 Bionic CPU, 3GB of RAM and 64/256 GB of storage.
The iPhone X carries a high price tag, starting at $999. iPhone X sales were lower than expected, which caused problems at Apple's supplier, including Samsung Display who produces the OLED displays for Apple.
It is still not clear what are Apple's plans for 2018, but it seems likely that Apple will introduce three new iPhones this year. The main model will still use an LCDs, but there will be two higher-end OLED models - a replacement for the iPhone X with a 5.8" AMOLED and a larger 6.3" or 6.5" variant. According to reports Apple wanted LG display to supply it with the larger OLED displays, but it is not clear whether LG Display will be ready with the quantities and quality Apple requires this year.
The OLED Apple Watch
The iPhone X is not Apple's first product to adopt an OLED display, though. In April 2015 Apple launched its first wearable device, the Apple Watch which used a flexible AMOLED display (made by LG Display). All Apple Watch products to date continue to use LGD's flexible OLEDs. OLED displays are especially suitable for wearable devices - as the displays are thinner and lighter than LCD displays, and are more power efficient (especially if you tweak the UI to suit the special OLED properties).
Apple OLED MacBook Pro
Apple's MacBook Pro range of high-end laptops started adopting an OLED Touch Bar instead of the traditional function keys in 2016. The display itself is either a 13" or a 15" LCD.
The OLED strip is supported by most of Apple's applications and can show commonly used emojis in messaging applications, bookmarks while you browse and other context-activated options. It also includes a Touch ID sensor that is activated for example when you wish to pay online (on supported web stores). Apple released an API to developers can support the Touch Bar in third-party applications.
The latest Apple OLED news:
ETNews: SDC sent 7.2" foldable OLED samples to Apple and Google
Korea's ETNews reports that Samsung has shipped foldable OLED display samples to both Apple And Google. According to the report, the displays sent to Apple were 7.2" in size (just slightly smaller than the Galaxy Fold OLED display).
This is hardly a surprise - it's highly likely that all smartphone brands are now looking into foldable displays for next generation devices - and all leading brands are also likely to want to design prototypes and start looking at displays.
WSJ: Apple to use OLEDs in all of its 2020 iPhones
The Wall Street Journal reports that Apple plans to finally drop LCD from its iPhones in 2020 - and to use OLEDs in all of the models.
WSJ also says that Apple plans to release an ambitious 2020 iPhone lineup with "a more flexible handset design". The 2019 lineup will be an "iterative change" from the current Apple lineup - and will still use an LCD in the lower-end model.
ETNews: Samsung to supply Apple with Y-OCTA OLEDs for some of its 2019 iPhones
According to Korean publication ETNews, Samsung is aiming to supply Apple with its latest Y-OCTA OLED panels for Apple's 2019 iPhones. Y-OCTA (or Youm On-Cell Touch AMOLED) is Samsung's term for its on-cell touch flexible AMOLED technology. 
Y-OCTA panels are thinner than Samsung's previous flexible Add-On Touch panels as the touch sensor is deposited directly on the encapsulation (TFE) layer. The optical features are also better as the touch layer is below the polarizer and enables the use of a non-ITO grid, there's no need for a support film (see image above) and the number of layers is lower.
ETNews: LGD to start shipping OLED panels to Apple in December 2018
According to ETNews, Apple has contracted LG Display to start producing OLED panels for its smartphones. LG Display will produce the new OLEDs at its E6 production line in Paju, and will start shipping panels to Apple in December 2018.
The report says that LGD will ship around 400,000 panels to Apple by the end of 2018. The cost of each panel is around $90. This deal is important for LGD, and also for Apple as it wants to diversify its OLED supplier base. According to other reports, these LGD panels will only be used as repair panels by Apple, and will not be integrated into new iPhones.
The Washington Post mistakenly blame OLEDs for low battery life in 2018 smartphones
The Washington Post's Geoffrey A. Fowler posted an interesting article in which he details how new smartphones are under-performing older ones in terms of battery life. Geoffrey puts 12 smartphones to the same test, and checks which ones dies first.
It is interesting that the new 2018 smartphones under performs similar smartphones released in 2017. Geoffrey's conclusion is that new display technology - high resolution OLEDs, are the culprit. The main reasoning behind that is that the iPhone XR (with its LCD display) performs better than the iPhone XS, even though the XR has a smaller display.
Ming-Chi Kuo: Apple to continue and use an LCD in its entry-level 2019 iPhone
In 2017 Apple introduced its first OLED iPhone (the iPhone X), and in 2018 its smartphone range include 2 OLED phones (the iPhone XS and XS Max) and one LCD phone. Earlier estimates suggested that in 2019, Apple's will move exclusively to OLED in all of its smartphones. But a new report suggests otherwise.
Known Apple analyst Ming-Chi Kuo says that in 2019 Apple will continue to use an LCD display in its entry-level smartphone. The 2019 range will include two OLED iPhones (5.8" and 6.5") and the LCD model will use a 6.1" display - a similar lineup to the one they have in 2018.
Several Apple Watch series 4 customers complain of a strong off-angle blue tint
Apple recently launched its latest smartwatch - the Watch Series 4. It seems that at least some customers are complaining about a strong blue off-angle blue tint on the new OLED display. Some of these customers say that the tint is stronger compared to previous generation Watch devices - and also stronger than the tint on the iPhone X and LG OLED TVs.
It's not clear whether this is a real issue or not at this stage - we only have heard of a few customers complaining so far. But this is interesting as Apple has adopted its new LTPO backplane technology in the Watch 4, which could be responsible for the stronger tint (Is this the beginning of LTPO-gate?). All previous Watch devices used flexible AMOLED displays made by LG Display. We do not know yet whether LGD is still the exclusive supplier, or whether Apple added Samsung Display as its second source (or even exclusive).
DisplayMate: The iPhone XS Max has the world's best mobile display, and it is produced by SDC
DisplayMate has posted a comprehensive review of the Apple iPhone XS Max display - a 6.5" 1242x2688 AMOLED display. DisplayMate has found that this display is highly impressive - with a close to text-book perfect calibration and performance. The display has been found to be on par with the Galaxy S9 and Note 9 display.
The high performance display led us to ask DisplayMate's Raymond Soneira about the producer of this display - and he confirms our estimation - the iPhone XS Max's display was produced by Samsung Display. In the past months we have heard many reports claiming that Apple contracted LG Display to produce this 6.5" AMOLED, and now we have proof that eventually Apple chose to keep Samsung as its exclusive supplier for Smartphone AMOLEDs, at least for now.
Apple launches two new OLED iPhones and the LTPO OLED Watch Series 4
As expected, Apple launched three new smartphones. The 2018-2019 lineup includes the OLED iPhone XS and XS Max and the iPhone XR which uses an LCD display.
The iPhone XS is the successor to the iPhone X - this phone sports a 5.8-inch 1125x2436 flexible notch-type AMOLED display (produced by Samsung Display), 4GB of RAM and 64/256/512 GB of storage.
IHS: Apple is developing a new LTPO backplane, may introduce it in future iPhones
IHS posted an interesting article which details a new backplane technology that Apple is developing. So-called Low-Temperature Polycrystalline Oxide (LTPO) combines both LTPS TFTs and Oxide TFTs (IGZO, Indium Gallium Zinc Oxide). LTPO is applicable for both OLED and LCD displays.
In LTPO, the switching circuits are using LTPS while the driving TFTs will use IGZO materials. This could lead to a power saving of around 5-15% compared to the currently-used LTPS backplanes. The main drawback of LTPO, however, is that the IGZO TFTs are larger and so the display density may be compromised. IHS says that Apple may introduce this into future iPhones - but it also says that LTPO will be limited to low-density displays at first which is a bit confusing.