Meaning of R in English
The letter r, used in a number of situations, but perhaps most usefully in the plural for swearing in front of the students in maths or science lessons without them necessarily realising. Example: Let us call the radii of the circles drawn by John r1 and r2, and those drawn by Jane r3 and r4. You can see that the sum of John's r's is larger than that of Jane's r's.
Slang English vocab. Английский сленговый словарь. 2012