Clause within a contract that allows the exit of that contract normally with stipulations. These are sometimes used in conjunction with fixed term tenancies and will normally allow either party to get out (normally with about 2 months notice) before the end of the new term.

For example: in an AST after the first 6 months is over when it comes to renewal either party (landlord or tenant) will often request that a break/release clause be entered into the agreement if they are unsure whether they will want to continue renting the property for the duration of the next 6 months.