Apache Tomcat is an open-source web server and servlet container developed by the Apache Software Foundation. It is designed to run Java applications and provides a platform for executing Java Servlets and JavaServer Pages (JSP). Tomcat is widely used for hosting web applications due to its reliability and ease of use. Tomcat supports the Java EE specifications and is often used in conjunction with other technologies like Spring and Hibernate. It can be integrated with various web servers, such as Apache HTTP Server, to enhance performance and scalability. Tomcat is popular among developers for its lightweight nature and robust features.