In One Minute : Apache Tomcat

Apache Tomcat is a free and open-source implementation of the Jakarta Servlet, Jakarta Expression Language, and WebSocket technologies.
Tomcat provides a "pure Java" HTTP web server environment in which Java code can run.

Tomcat started off as a servlet reference implementation by James Duncan Davidson, a software architect at Sun Microsystems.

The Components of Tomcat are,
Catalina
Coyote
Jasper
Cluster
High availability
Web application

Catalina is Tomcat's servlet container.
Coyote is a Connector component for Tomcat that supports the HTTP 1.1 and 2 protocol as a web server.
Jasper is Tomcat's JSP Engine.
Cluster component has been added to manage large applications.
A high-availability feature has been added to facilitate the scheduling of system upgrades without affecting the live environment.
Web application has added user- as well as system-based web applications enhancement to add support for deployment across the variety of environments.

Official Website :- https://tomcat.apache.org/