Commonly known as a perf pip. There are a number of set configurations and they are normally collected as a block of 8 plus selvage across the central gutter. The block may or may not contain the inscription, The perf pip is often sliced off when the sheets are trimmed.
They are a guide for the perforation process. They are printed as part of the normal printing process and at the same time a holes are punched in the sheets in the perf pip locations. Originally the punches were part of the printing plates but this was a weakness which caused the plates to crack. As a result the punches were incorporated into printing machine. I'm not entirely sure of exactly how they work.
In Britain, pips usually referred to the emblems army personnel had on their epaulettes to signify rank. If I remember correctly, it was one pip for a lieutenant - that would be pronounced as leftenant - two for a captain and three for a major. So using the term for small dots is not too outrageous.