What is the definition of a mere puff?

Mere Puff is a statement, which by its nature, and in the context in which it is made, is not intended to have legal relation. It is used in contract law to describe the statements of a contract. When a statement is a "term" and one of the parties breach it then it is going to be legally liable to the other party. If a term is just a representation (or mere puff) the remedies are going to be different.