A Commitment Mechanism is a tool or technique that lets people pre-commit to something. an assurance contract is a Pre-Commitment done between several people which is conditional on other people also pre-committing.
Many commitment mechanisms incentivize following through on a commitment by penalizing failures to do so. For example, having to pay some amount of money, or automatically posting an announcement to your social media that you failed.
See also: beeminder.com