Term for "exact type turned into a dyn"?

I think I get it now. "Unsized Coercion" refers to precisely those 3 transforms in Type coercions - The Rust Reference

"type erasure" is slightly less formal and includes T -> dyn and T -> *mut ().

Thus, [T; n] -> [T] is unsized coercision but not "type erasure", while `T -> *mut ()" is type erasure, but not unsized coercision.

^-- This is your "argument" right ?