Workflow will be triggered whenever the record is created.

created, and every time it’s edited:

Workflow will be triggered whenever the record is created and updated.

created, and any time it’s edited to subsequently meet criteria:

Workflow will be triggered whenever the record is created and updated records which previously didn’t meet the criteria.

Check this for more clear definition

https://www.infallibletechie.com/2013/05/difference-between-created-created-and.html