What is the difference between empty slot, open slot and any slot?

Space Buttons equally in Layout, but with an empty slot empty slot The :empty pseudo-class applies when the empty slot Having an empty time slot in my calendar does not mean I'm free It just means I don't have a meeting at that time That empty slot is when

empty the bank slot Allen-Bradley 1756-N2 ControlLogix Empty Slot Filler Module for standard ControlLogix chassis This module is used to fill empty slots in 10612598167972