Extras is a mechanism in Amazon Linux 2 to enable the consumption of new versions of application software on a stable operating system that is supported until June 30, 2023.
Extras help alleviate the compromise between the stability of the OS and freshness of available software. For example, now you can install newer versions of MariaDB on a stable operating system supported for five years. Examples of extras include Ansible 2.4.2, memcached 1.5, nginx 1.12, Postgresql 9.6, MariaDB 10.2, Go 1.9, Redis 4.0, R 3.4, Rust 1.22.1.
https://aws.amazon.com/amazon-linux-2/faqs/#:~:text=Extras%20is%20a,3.4%2C%20Rust%201.22.1.