TwiML
Twilio's XML dialect that tells the platform what should happen during a phone call or text message.
TwiML (Twilio Markup Language) is the XML-based set of instructions Twilio fetches when a call or message comes in. Verbs like <Say>, <Play>, <Dial> and <Gather> describe step by step what should happen: read out a sentence, forward the call, record, collect key presses. When Twilio launched in 2008 under Jeff Lawson, this very idea — telephony driven by an ordinary web request — was the company's big breakthrough.
The server Twilio calls answers with TwiML, either static or generated on the fly in any language. The model is the same as a webhook: Twilio asks your code what to do next. SMS and voice use different verbs but rest on the same basic idea.