Free Float and Total Float Definition

Free Float The amount of time that a schedule activity can be delayed without delaying the early start date of any successor or violating a schedule constraint.

Total float :
The total amount of time that a schedule activity may be delayed from its early start date without delaying the project finish date.

Example
If activity A has a duration of 10 days and is parallelly with activity B which has a duration of 20 days, activity A has 10 days of total float. Meaning, it can be delayed up to 10 days without any effect on the project.
However, if activity A is delayed by 15 days, there is now a negative float situation: -5 days. This reflects the fact that the project will now take 5 days longer than anticipated.