Lacking means missing something that is needed. Lacking in confidence, sadly lacking, found lacking.
It takes in when followed by a quality — lacking in detail, lacking in warmth — and no preposition when followed by a thing: lacking the funds. Found wanting and found lacking both mean judged inadequate, and the first is the older phrase. Note that lacking as a bare adjective is a quiet way of saying something was not good enough: the response was lacking.
1adjectivelackingMissing something that is needed.
“The team has talent, but it's lacking a strong leader.”
lacking is a state of absence.
Practised in Everyday Adjectives