Hi,
We basically wants the average of the time spent by this scheme (using n call), to be less than nL.
So in a sense it represents a constraint that our system needs to obey. In class we have discussed an example of scheme with a constraint, e.g. the average power constraint in AWGN.
For the first few sub-questions, you can just think of it as a positive real number. In the last sub-question, you are asked to find the optimal L to maximize the amount of information transferred per time unit.
Best,
Reka