Informal To provide with information that is essential or newly acquired. This is the correct definition of the phrase "Fill You In".
Life's going well (getting better) and I want to fill you in on the details.
by ChrstnSl March 15, 2013
1 more definition
To fight and possibly win a fight against you
you carry on like that, and I'll fill you in
by npeckt September 23, 2009