“Leakage” in context

I have been reading a text about spotting lies by analysis of voice, gestures, etc., and cannot understand the word leakage in this sentence:

... clues of emotions... These are what provide leakage or deception clues.

Is it related to clues (leakage clues or deception clues), or does it mean leakage on the liar’s side (unintentionally revealing he is lying)?

All dictionaries mention only two meanings of leakage: physical (such as of liquid) or deliberate disclosure of information. Neither fits here for me.

You mention two senses of leakage; but the sense appropriate here is analogous to sense 3 at above link:

an undesirable flow of electric current through insulation

Your text is suggesting that the liar's body language involuntarily leaks information to the careful observer.

Note, “provide leakage or deception clues” is not saying “provide leakage clues or deception clues”, but instead “provide leakage; or, clues to deception”.