I think I have heard this expression in/on a television show.
I'd like to know if it actually exists, please.
If so, does it mean "things that you don't have"?
I've just googled for this phrase. It seems that it is part of a song, at least I came across many lyrics containing this phrase.
You are right with your suggestion.
It means things that you don't have.
They continue to lack a certain warmth in commucation with other people.
The pupils were showing a lack of interest in this subject.