Refers to a careless mistake or something left undone due to insufficient attention. Often used in the phrase 手抜かりなく (without oversight) or to describe a failure in preparation or execution.
Please proceed with the preparations so that there are no oversights.
His report had many omissions.
Compound of 手 (hand, action) and 抜かり (neglect, oversight), from the verb 抜かる (to be careless). The exact historical derivation is uncertain, but the word has been used since at least the Edo period.