Chatbots are programs that conduct conversations through text or audio to simulate human interaction. There are two main types of chatbots: custom chatbots that are built using programming languages and embedded into custom apps/websites, and third-party chatbots built using software like Manychat or Chatfuel that operate on messaging platforms like Facebook Messenger. Messenger bots are a type of third-party chatbot that can only be built for Facebook pages using platforms approved by Facebook. The document provides information on chatbots and how to get started building messenger bots for Facebook.