I can't give a legal definition not being a lawyer. So here is Wikipedia's: A person's primary residence, or main residence is the dwelling where they usually live, typically a house or an apartment. A person can only have one primary residence at any given time, though they may share the residence with other people. A primary residence is considered as a legal residence for the purpose of income tax and/or acquiring a mortgage. Criteria for a primary residence consist mostly of guidelines rather than hard rules, and residential status is often determined on a case-by-case basis. Tim