Automatic autofocus (AF-A)
Automatische autofocus (AF-A) · Technique
The camera automatically switches between AF-S and AF-C depending on whether the subject moves.
Mainly found on Nikon and Sony cameras. Useful when you're unsure whether a subject will stay still or start moving. The camera detects motion and switches to continuous AF. Not always reliable: for sport you're better off choosing AF-C deliberately, for portrait use AF-S.
Tools that help with this: