What it means
A caveat (Latin for "let them beware") is a notice lodged with the land titles office claiming an interest in a property. Once registered, it acts as a roadblock: it prevents the owner from selling, transferring or mortgaging the land without first dealing with the caveator's claim. In Australia a caveat must be supported by a genuine "caveatable interest". Lodging one without proper grounds can expose you to compensation claims, so legal advice is usually wise before lodging.
How it's used
She lodged a caveat over the house to protect her claim to a share before her ex could sell it.