Free snack or sneaky trap?

Loose pieces are invitations. A piece is hanging when it can be taken without sufficient compensation.

A hanging piece is a piece you can win because its protection is missing or not enough. Start by looking for pieces that your side already attacks. A bishop sitting alone is only a target if you can actually reach it with a legal move.

Undefended and hanging are not quite the same. An undefended piece may be out of reach. A defended piece can still be won if its defender is pinned, overloaded, or unable to recapture safely. Your job is to find a capture that works after the reply, not merely count nearby pieces.