Bump
White bumps into the Black stone. A natural local response is usually to stretch to a or b. A common term for this move is butting play.
The Japanese term is tsukiatari.
The bump is not a very usual move, but it has its uses.
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Example 1: Kitani joseki
There is an interesting branch of 3-4 point joseki (invented by Kitani Minoru) starting with a bump: