Ogust is a bridge convention used after a weak two bid by responder to gauge the strength of the weak two bidder's hand. This convention is named after Harold A. Ogust from the US, and is also known as the 'Blue Club response' from the bidding system developed by Benito Garozzo.
After any weak two opening bid, a forcing relay bid of 2NT by responder asks opener to describe the general strength and quality of their hand. Responder usually has around the points for an opening bid and is interested in game, although it does not guarantee trump support.
The standard responses to the Ogust convention, as listed in The Official Encyclopedia of Bridge and Goren's New Bridge Complete, are:
2♦/♥/♠ - (pass) - 2NT - (pass) -
The definitions of "minimal" and "maximal" hands and "poor" and "good" suits are matters of partnership agreement. Many players regard a "minimal" hand as 6-7 HCP and a "maximal" hand as 8 or more HCP. There's more variation in the interpretation of "poor" and "good" hands. Partnerships that are strict in their preempts tend to regard suits with only two of the top three or three of the top five cards as "poor" while partnerships that preempt with poorer suits typically describe such suits as "good."
After knowing the quality of opener's hand, responder can set the contract.
There are many variants to the Ogust convention. Some partnerships reverse the meaning of 3♦ and 3♥, which is Ogust's original formula.
Ogust's original formula also did not include the 3NT bid showing a solid suit.
Other variants define a "poor" suit to be one of the top three honors, and a good suit to be two of the top three honors, with "solid" suit denoting AKQ, or define minimum strength to be 6-8 HCP, and maximum strength to be 9-10 HCP (Benji Acol)