Second Line Clamp
The clamp on threatens to watari underneath with a or start a second line capture with b.
Depending on the context (hinted at by the circled points), Black can either resist at a, connect at b or even play c (but this leaves in atari after white a.) If Black can't resist, the clamp is a big endgame play.
To resist black needs to capture directly or in a ladder. A net is not enough since + will be captured then. (Alternatively, if is very stable - more than in this diagram -, black may force once or twice and simply capture .)