A vaguely worded statement or advertisement which is not intended to be taken seriously. It is not specific enough to be an offer .
Case example: Carlill v Carbolic Smoke Ball Co (1893)
The company claimed in an advertisement that no-one using its smoke ball would get flu. If anyone using the smoke ball did get flu then they would be compensated by the company which had deposited £1,000 with their bankers against this eventuality. It was held that the first statement on its own was a mere puff but the later statement about depositing money turned the advertisement into an offer.