Question

is speed represented by the instantaneous velocity

Answer 1

or is it represented by the time interval?

Answer 2

Speed is time divided by distance and is a scalar quantity meaning it only requires a magnitude for a description, Velocity is a vector quantity which means it requires both a magnitude and specified direction. Instantaneous velocity is velocity at a particular moment. So speed would be the magnitude of instantaneous velocity without the direction.\[Speed = Distance/Time\] I hope this helps.