Assist train

A group or team of multiple players in which only one player selects the target to attack while the others select the same target with a /assist macro or other means.

Exploiting such macros in PvP results in a quick and irresistable vaporization of hostile players.

This is how an assist train macro might work for assisting with the spell "fireball" where "1" is the group leader

/assist 1
/cast fireball