Kick your Piece?

I'm a complete beginner. When I run a game analysis and the "coach" says a move was bad because it allows the opponent to "kick" my piece, what does that mean? I look at the board, and I can't figure out why the move was wrong. The knight I moved is not under any attack or threat, so I have no idea why the move was considered an "inaccuracy". 

Can someone explain, please, what "This lets your opponent kick your piece" actually means? Thanks for any help with this. 

I took a screenshot, but I don't know how to post it here. 

To "kick" a piece means to attack it (or threaten to imminently attack it) either with a threat to capture it or with some other advantage potentially accruing to the attacker (the "kicker"), and typically resulting in the "kicked" piece moving in order to avoid or counter the threat.  The "kicker" is typically a piece of lesser value than the kicked piece, or a pawn.

Glossary of Chess.....(see 'kick')...

https://en.wikipedia.org/wiki/Glossary_of_chess#K

Improving Your Chess - Resources for Beginners and Beyond...

https://www.chess.com/blog/RussBell/improving-your-chess-resources-for-beginners-and-beyond

https://www.chess.com/blog/RussBell

Thanks. I will take a look at the glossary. 😁

How long has that term been common in Chess? I used to play a lot in the 90's and never heard it nor saw it used in any of the books I read, but coming back to play some recently I like OP was puzzled by the term as used by the chess.com coach ai. Do people use the term normally in conversation as well?

The term is not a "standard" chess term and is not commonly used in chess.  It is a colloquialism, a slang term, used very infrequently.