Definition of fat-finger:
(v) :
(transitive, humorous, informal) To type (something) erroneously on a keyboard, keypad, or touchscreen by accidentally pressing with a finger one or more keys other than the intended one.
(n) :
Alternative form of fat finger. [(idiomatic, humorous, informal, also attributively) A supposed cause of typographical errors, especially keyboard errors, caused from erroneous key presses or typing errors on touchscreen devices.]