Java Servlets are server-side components that extend the functionality of web servers by providing dynamic response to client requests through a request-response programming model. Servlets are essentially Java classes that can be used to handle HTTP requests and generate responses dynamically. They are used in modern-day web applications for server-side programming, communication with databases, serving files, handling session management, and authentication.

Servlets are platform-independent and can be deployed on any web server that supports the Java Servlet API. The life-cycle of a servlet is managed by the web container/server that executes the servlets. Servlets interact with clients through the HTTP protocol and use the same set of request and response objects available in the HTTP protocol.

Some of the notable features of Servlets include support for multithreading, configurable initialization parameters, session tracking, and security support. They are extensively used in developing enterprise web applications.

Servlets are an integral part of the Java EE framework and are commonly used in combination with other Java Enterprise Edition technologies such as JavaServer Pages (JSP), JavaBeans, and EJBs. Learning Servlet programming is essential for anyone who wants to develop modern-day web applications using Java.