What is the difference between @ and # tags ?
Nothing and that the best part, you can define to anything you want it to be.
While @KC is technically correct, the two tag types stem from GTD (Getting Things Done) when working on projects. The # symbol is a label and you can have one or more per list item depending on how you want to organize it. The @ symbol is typically used once per item and gives the item a context or place. You can then filter on these accordingly. I recommend looking up GTD if you wish to learn more.
I like the GTD Use-Case of the “@”-Symbol. Maybe it would be nice to assign tasks to other Users in shared documents with it. For example “@Anna”.