preposition

at

Used to identify a particular place, time, activity, or target.

We meet at the library before walking to the concert.

Etymology

Old English æt placed something at or near a point. Modern uses extend that locating function to a point in time, an activity, or the target of an action.

More examples

The train leaves at six o'clock.
She is at work until five.
He aimed the flashlight at the dark doorway.

Similar words

in: Usually places something within an area rather than at a point.
near: Indicates proximity rather than a particular location itself.