A chatbot is a service, powered by artificial intelligence, that you interact with via a chat interface.
The Complete Beginner’s Guide To Chatbots
Matt Schlicht

This is a bad definition, at least for the current wave of chatbots. 95% of chatbots out there right now are not AI based. Chatbots are micro apps delivered via a messaging API instead of a web or native app. A small number of them (Siri, Google Now, Cortana etc) use machine learning or artificial intelligence in the same way a small number of mobile apps use artifical intelligence.