is counter-atari, responding to the atari of by giving atari back. This is often a better alternative than the heavy connection at a.
naturally captures, after which (or a, depending on the overall position) gives atari. then connects.
Black will have a pincer stone at one of the points a to f. With a close pincer (a or b) White now usually connects solidly at p, with the aim of extending to the marked point. With the more distant pincers d and e White makes the trumpet connection at q for better shape (the other two pincers are rare in this pattern).