For the text chat, it's different in the way that it lets one make their own 'servers' without having to run the actual hardware server 24/7, free of charge, no need to battle with NATs and weird nonstandard ways of sending images, etc.

The big thing is the voice/videoconferencing channels which are actually optimized insanely well, Discord calls work fine even on crappy connections that Teams and Zoom struggle with.

Simply put it's Skype x MSN Messenger with a global user directory, but with gamers in mind.