LEDs (light-emitting diodes) are the tiny, colored, indicator lights you see on electronic instrument panels. They're much smaller, more energy-efficient, and more reliable than old-style incandescent lamps. Instead of making light by heating a wire filament till it glows white hot (which is how a normal lamp works), they give off light when electrons zap through the specially treated ("doped") solid materials from which they're made.
An OLED is simply an LED where the light is produced ("emitted") by organic molecules. When people talk about organic things these days, they're usually referring to food and clothing produced in an environmentally friendly way without the use of pesticides. But when it comes to the chemistry of how molecules are made, the word has a completely different meaning. Organic molecules are simply ones based around lines or rings of carbon atoms, including such common things as sugar, gasoline, alcohol, wood, and plastic