A .thrift file is a definition file used by the Apache Thrift framework. Apache Thrift is an interface definition language (IDL) and binary communication protocol used for defining and creating services for multiple languages. The .thrift file defines the data structures, interfaces, and services that will be used in a Thrift application. It specifies the data types, fields, methods, and exceptions that are part of the service contract. The Thrift compiler then uses this definition file to generate code in various programming languages, such as C++, Java, Python, PHP, Ruby, Erlang, Go, and more. This generated code includes the necessary classes and functions for serializing and deserializing data, as well as for making remote procedure calls (RPCs). The primary purpose of a .thrift file is to enable cross-language communication and interoperability between different software components. It allows developers to define a service once and then implement it in multiple languages, ensuring that all implementations adhere to the same contract. This simplifies the development of distributed systems and microservices architectures.