Simply put Django is a framework for building web applications and websites. But what does that actually mean (without going into technical jargon)?
Django provides a set of tooling to easily accomplish the tasks required to create different webpages populated by data stored somewhere else (typically a database) or have pages that can take data from the browser and store it in a database.
Django is designed to be 'batteries included', which means common tasks such as allowing user sign up are easy to setup and require little work by us as software developers. Finally and perhaps the best thing is Django is completely run by the community, this means people volunteer their own time to make improvements and help others; it also means that a single company is not able to change the direction of Django meaning it has and will be around for the long haul.