This article is from the Magic: The Gathering Rules FAQ, by Patrik Linell (pls@claymore.nu) with numerous contributions by others.
The affliction that makes creatures unable to attack and tap for
abilities during the turn in which they come into play (and the following
opponent's turn). The term was only officially used for 5th Edition rules,
but earlier editions did mention it. This condition has no name now, so
most people still use summoning sickness, although it's technically
incorrect. Creatures that used to be "unaffected by summoning sickness" now
have "haste" instead. It works the same.
 
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