https://tokio.rs/tokio/glossary

send trait

The Send and Sync traits are marker traits related to concurrency provided by Rust. Types that can be sent to a different thread are Send. Most types are Send, but something like Rc is not. Types that can be concurrently accessed through immutable references are Sync. A type can be Send but not Sync — a good example is Cell, which can be modified through an immutable reference, and is thus not safe to access concurrently.
For more details, see the related chapter in the Rust book.

pin

A Rust value is “pinned” when it can no longer be moved in memory. A key property of a pinned value is that pointers can be taken to the pinned data and the caller can be confident the pointer stays valid. This feature is used by async/await to support borrowing data across .await points.