JMeter is an open source load testing tool that is used to simulate heavy loads on a server, network or object to test its strength or to analyze overall performance under different load types. It was developed by Apache Software Foundation and is written in Java.

With JMeter, you can simulate the behavior of multiple users using different protocols such as HTTP, FTP, SMTP, and more. You can create a test plan that contains one or more thread groups, each representing a group of users who perform a specific set of actions.

JMeter provides a graphical user interface that allows you to create, run, and monitor test plans. You can configure a wide range of settings for your test, such as the number of threads, the ramp-up time, the duration of the test, and the type of reports you want to generate.

JMeter also provides a number of plugins that extend its functionality, such as the ability to test web services, databases, and messaging services. It supports a wide range of load testing scenarios and can be integrated with other tools and frameworks such as Selenium, Jenkins, and Apache Maven.

JMeter is widely used in the industry to ensure the performance and scalability of web applications, especially during the development and testing stages. It can help developers identify performance bottlenecks, track down issues, and optimize their web applications for different load scenarios.