Answer:
It is a legal term which covers who pays for what in the event of litigation. In a construction contract setting, generally, the owner will require the contractor to indemnify, defend and hold them harmless in the event of a claim attributable to the work. Separately they mean:
Indemnify - reimburse costs for defense of the claim
Defend - control the defense of the claim
Hold Harmless - agreement to not hold the owner liable for costs the contractor incurs as a result of defending the claim