"Concurrent copies" referrs to all physical copies of a product held at any given time. If you have bought an A4 map of an area and print it twice without throwing any of the prints away, then you are holding two concurrent copies. If you print it three times in total but throw away the first two before printing the third you only hold one concurrent copy.
If you decide to "abuse" the office printer and pre-print 20 copies of your map for the future, then you are holding 20 concurrent copies at the time you finish printing. This would mean you are 18 copies over the limit we allow and you would be in breach of your license, unless you purchase a permit for extra copies from us. The cot of extra copy capacity depends on the product size and the latest full (and easy) calculation can be found in our license schedule.
We are relatively unique in that we trust our customers to create copies of their maps and stick within the rules we have set. Most producers of ready printed mapping forbid the copying of their maps outright, including some of the biggest names in the business.