Position
A position is the job a shift is staffed for rather than the person who fills it: the till, the grill, the bar, the reception desk. Shifts are drawn against positions, and people are then assigned to them.
Why it matters in a small workplace
Counting heads is not the same as being covered. Three people on shift is not cover if all three are on the floor and nobody at all is on the till.
How Weeksort handles it
Positions are the rows of the weekly grid a manager builds in, one row per position with the days across the top. Each position lists the qualifications it requires, and only people who hold all of them can be scheduled to it.