Groovy is a dynamic language for the Java Virtual Machine that aims to provide productivity features like closures, builders, and metaprogramming while leveraging Java's capabilities. The document discusses why developers should use Groovy to build Atlassian plugins, noting features like closures, domain specific languages, and builders that improve productivity. It addresses myths that dynamic typing reduces IDE support and that scripting languages are unprofessional. Code examples demonstrate how Groovy code can be more concise and readable than equivalent Java code.