Over weak two-bids -

The Ogust structure is used by responder to discover what partner's hand and suit looks like when opener opens a weak two.

Responder uses 2NT to ask for a description. Opener's rebids are:

3C bad hand (lower half of range usually 5-7), bad suit (good suit includes 2 of the top 3)

3D bad hand, good suit

3H good hand, bad suit

3S good hand, good suit

3NT all top three honors (thus good hand)