What is an OLED display?
An OLED display uses a new technology called OLED (Organic Light Emitting Diodes). OLED screens are brighter, more efficient, thinner and feature better refresh rates and contrast than LCD or Plasma.
OLEDs are made by placing thin films of organic (carbon based) materials between two conductors. When an electrical current is applied, a bright light is emitted. Since the OLED materials emit light, a backlight is not required (unlike LCDs).
OLEDs in mobile phones
Mobile phones that boast OLED screens are rapidly becoming more prevalent, with an estimated 250 million AMOLED screens produced in 2015 - mostly to satisfy demand from mobile phones. Samsung has been using AMOLEDs in its high-end phones for many years, and most phone makers are also starting to adopt OLED displays (including Apple, according to reports, in 2017).
Mobile phones that use OLED displays do not seem very different at first glance, and their outer appearance can be hard to tell apart from an LCD display phone. Their quality, however, is immeasurably better. The latest generation OLED displays outperform LCDs in all parameters...
Samsung started to adopt flexible OLED in some of its high-end phones. These displays can be curved and Samsung adopted a design in which the OLED is curved around the edges. This proved to be a very popular design and starting in the Note 7, Samsung exclusively uses curved edge flexible OLEDs.