An accessibility feature in Windows. StickyKeys allows a user to press and release a modifier key (Shift, Ctrl, Alt, AltGr, etc.), and have it perform its function on the next character pressed, rather than having to hold the modifier key down. For example, with StickyKeys enabled, one could simply tap the Shift key, and then hit a, and the result would be A. In other words, as Microsoft says in their help file, "StickyKeys enables simultaneous keystrokes while pressing one key at a time."
The same type of feature is used with accent characters on keyboards with non-American layouts. On a non-American keyboard, the user can press a special accent key (for example, `) and then a compatible letter (e) and the output would be è.
StickyKeys can be accessed by going to the Control Panel, opening Accessibility Features, and looking at the Keyboard tab.