Do "slots" on the availability calendar mean Clients or Time Slots?

So I had a client try and reach out to me about walking their dog tomorrow. I have 1 dog walking "slot" tomorrow but they requested 2 times. It ended up not working because I could only do 1 out of the 2 times. So does "slot" simply mean "client" on Rover's Availability Calendar? And is there a way to customize further?