Clashing is a system found in some games, including Guilty Gear, World Heroes 2 Jet, Arcana Heart, and Melty Blood, among others.
When strike hitboxes mutually collide, a clash system will cause these attack hitboxes to disappear (as opposed to what happens with trading hits). The mechanism for this varies; in Kidō Senshi Gundam and WH2J, both players will mutually widen their range. In Rival Schools, it will add one stock to each player’s power meter. In GG, AH, and MB, the stun after a clash can be cancelled via another move. Also, in AH and MB, there are moves that have clashing implemented as a hitbox.