Active Calories VS Total Calories during a workout

I'm fairly new to the Apple App- I was a Fitbit user and Fitbit reflected Fat burn, active minutes and Peek time during a work out. Apple app reflects Active Calories and Total Calories during a work out and I am not able to find an answer to define the difference. what is the difference in a work out from Active vs Total. I am still on the fence about this app, fitbit showed when during my work out my heartrate increased, and clearly reflected the calories -