Anchor is a framework for quickly building secure Solana programs.
With Anchor you can build programs quickly because it writes various boilerplate for you such as (de)serialization of accounts and instruction data.
You can build secure programs more easily because Anchor handles certain security checks for you. On top of that, it allows you to succinctly define additional checks and keep them separate from your business logic.
Both of these aspects mean that instead of working on the tedious parts of raw Solana programs, you can spend more time working on what matters most, your product.