sOLED
In short: sOLED stands, depending on context, for stacked OLED technology in which subpixels lie on top of each other instead of side by side.
In more detail: The term is not used consistently. It usually means further developments of OLED technology in which layers are stacked to improve brightness, lifetime and resolution.
In Depth
Note
Manufacturers use different marketing names (for example tandem OLED, QD-OLED). For purchase decisions the technical data count: brightness, burn-in protection, warranty. See LED, monitor.