The phrase in arabic is 'مقصر في شيء', it literally means 'deficient in something'. So for example, if a wife said it about her husband, it would mean that he's doing some of what is asked and expected of him, but not enough, or not to her liking. A friend can also say it to a friend, it may mean that he hasn't asked about his health, work or even life as often as usual; he is not caring as is expected of him.
It can also mean not helping, not being there, a lack of presence, a lack of doing what you should be doing towards someone/something.
A government or a company can also be a victim of this, towards their people and employees respectively.
It's a criticism, usually said out of love.