Twilio’s APIs allow developers to reinvent communications with things like programmable phone calls, SMS or intelligent chatbots. Developers can build applications to interact with their users and react to their responses. To respond to events like incoming messages, you can define a webhook URL. A webhook is an HTTP request that Twilio performs to find out what the reaction to a Twilio even like an incoming SMS should be. Your defined HTTP endpoints have to respond with a Twilio-understandable configuration language called TwiML (Twilio Markup Language).These endpoints can be hosted anywhere as long as they’re available publicly and accessible by Twilio’s infrastructure.