Final answer:
A variation in innervation of intrinsic hand muscles is an abnormal deviation from the usual neural patterns of the muscles responsible for precise movements such as typing and writing.
Step-by-step explanation:
A variation in innervation of intrinsic hand muscles refers to any abnormal or uncommon deviation from the typical innervation patterns of the intrinsic muscles of the hand. These muscles, which include the thenar and hypothenar muscles, lumbricals, and palmar and dorsal interossei, are essential for the fine motor control required for precise movements such as typing and writing. They are responsible for flexing, extending, abducting, and adducting the fingers, and both originate and insert within the hand itself.