use consistent terminology

I did not see other traits using the "interface" word

library/core/src/async_iter/async_iter.rs

@@ -2,7 +2,7 @@ use crate::ops::DerefMut;
 use crate::pin::Pin;
 use crate::task::{Context, Poll};
 
-/// An interface for dealing with asynchronous iterators.
+/// A trait for dealing with asynchronous iterators.
 ///
 /// This is the main async iterator trait. For more about the concept of async iterators
 /// generally, please see the [module-level documentation]. In particular, you

library/core/src/iter/traits/iterator.rs

@@ -14,7 +14,7 @@ use super::super::{
 
 fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
 
-/// An interface for dealing with iterators.
+/// A trait for dealing with iterators.
 ///
 /// This is the main iterator trait. For more about the concept of iterators
 /// generally, please see the [module-level documentation]. In particular, you