Indemnification is a contractual obligation where one party (the indemnitor) agrees to compensate another party (the indemnitee) for specified losses or damages, often including the cost of legal defense. Construction contracts almost always include indemnification provisions: contractor indemnifies owner against claims arising from contractor's work; subs indemnify GCs against claims arising from sub work.
The scope of indemnification depends on the form: limited (indemnify only for indemnitor's own negligence), intermediate (joint negligence), or broad-form (regardless of fault). Many states limit broad-form indemnification through anti-indemnity statutes specific to construction contracts. Indemnification is typically backed by the indemnitor's general liability insurance, which is why contracts often require additional-insured endorsements running to the indemnitee.