It’s called “make it slow”. More specifically, a comparison of a long array/slice of strings, where each element has some information about increasingly narrower scopes.
One possible TypeId could look like this:
[rustc_id, cargo_id, crate_id, crate_version, module_id, ..., fn_id, struct_id, generic_id, ...]
rustc_id is shared across all crates/etc so uses very little space, cargo_id is also generally shared across all crates so also uses very little space, crate_id is per crate, so uses a little more space, but still very little, and so on.
If you were to concatenate the whole thing it would quickly get huge, but because we can reuse many of these across most types, it ends up getting rather small.