Difference between FVector & TossVelocity and float TossSpeed?

What is the difference between FVector & TossVelocity and float TossSpeed in UGameplayStatics::SuggestProjectileVelocity method?

Firstly remember that a velocity is a vector, so it’s telling us the direction. The TossSpeed is just a float which is the assumed speed we are launching at. You must pin-down either speed or direction or there are an infinite number of combinations of elevation and speed that lead to a successful hit.

I hope this makes sense