I struggle to understand wasm, though I'm interested. What does this part mean?

> Internally, it uses the wasmtime runtime to configure, initialize, and run the Wasm modules.

What is wasmtime? I looked at its page and couldn't figure out what they mean by a wasm runtime. I thought the runtime was in the browser. Wouldn't a user just need to compile and just a binary?

It is a runtime for wasm. Wasm is not executable in the same way an x86 binary is. It needs to run in a vm. Wasmtime is one such vm. In a browser context that vm is v8.

https://github.com/bytecodealliance/wasmtime