Dynasty Fantasy is a game mode in which you keep your players from season to season.
Dynasty leagues are a long-term project for each fantasy manager involved. There is a stronger sense of ownership as you can build and manage your team over multiple seasons. It’s more like real-life, because franchises are built over time. You’ll have way more satisfaction when you’re succesful.
There is still a draft in Dynasty Fantasy. But in this case managers get to pick from a pool of rookies and free agents. There can even be a separate draft for both. And draft picks can be traded as well.
A keeper league is similar to a dynasty league. The biggest difference is that you only keep a few players in a keeper league. Whereas you retain all or most of your players in dynasty.