What does shell-and-core mean for a restaurant fit-out?

A shell-and-core unit is handed over as bare structure — you build everything: mechanical, electrical and plumbing, kitchen services, finishes, the lot. A fitted or ex-F&B unit comes with some of that in place. The difference in capital cost between the two can be very large, so "what state is the unit handed over in" is one of the first questions to ask, because it changes the budget more than almost anything else.

From Restaurant Lease and Fit-Out: The Traps That Sink Operators — the full reading, with the method behind this answer.