In project management, total float refers to the amount of time a task can be delayed without affecting the project's overall completion date.
Free float refers to the amount of time a task can be delayed without impacting the start date of its successor tasks.
In simpler terms, total float considers the project end date, and free float considers the start of subsequent tasks.
4 minutes in, this video does a good job illustrating the difference betweenthe free and total float
Notice how task F has a free float of 2, which means it delays NO OTHER tasks, but also a total float of 3 meaning you can create a delay up up to 3 (which does delay G) but still keeps us on track for the TOTAL project.