Interpreters are programs that can directly execute instructions written in a programming or scripting language without requiring the source code to be compiled first. They are used to executing programs written in languages such as Python, Ruby, JavaScript, and PHP. Interpreters read the source code of a program one line at a time and execute instructions immediately, which makes them well suited for programs that require rapid response or interactivity. There are two main types of interpreters: byte code interpreters and source-to-source interpreters. Byte code interpreters directly execute the binary instructions of a program, while source-to-source interpreters translate the source code of a program into another language, such as assembly language or machine code, before executing it.