how to understand the simulation time and time-step

[jixian01]

Hello everyone, i am new to carla and have one question regarding the statement (below mentioned) in carla docu:
how to understand the simulation time and time step mentioned in the statement? Is this same as rendering frame?

"There is a difference between real time, and simulation time. The simulated world has its own clock and time, conducted by the server. Computing two simulation steps takes some real time. However, there is also the time span that went by between those two simulation moments, the time-step."

Thank you for your help!