Starknet is a Validity Rollup Layer 2. It provides high throughput, low gas costs, and retains Ethereum Layer 1 levels of security.
Given a sudoku puzzle, verifying a solution is easier than solving from scratch. If our goal is to convince people of the statement “this puzzle has been solved”, we can save a lot of computation by having one person compute a solution and then propagate it for others to verify. In this strategy, each computation of a solution becomes a one-time event which does not require replication by society. In a similar vein, Starknet scales Ethereum by replacing heavy L1 computation with lighter (hence cheaper!) L1 verification using STARK proofs computed off-chain.