Agile is not one ‘thing’ but a number of approaches or methodologies to develop faster. Think about Scrum, Kanban and other frameworks. The Wikipedia definition describes the broader view. But agility is about one word in the dictionary definition: Adaptable! For me, agility is being able to change course as quickly as possible. Your IT should be like a speedboat, not an oil tanker. Mind you, I am talking more about the manoeuvrability in this case than about speed.