This is a single jump, in a competitive auction or by a passed hand, showing length and strength in the suit bid and primary support for partner (nine or more cards between the two suits). It is forcing for one round.
In the first auction, 3♣ cannot be a strong jump shift because West passed as dealer. In the second auction, many pairs are happy to give up on the strong jump shift after the overcall and play this as a fit-showing jump. In either auction, West might hold:
One benefit of the fit-showing jump is that it enables partner to judge whether a two-suit fit is present.