This is the ship name for Enjolras and Grantaire, two of the barricade boys from the book/play/movie Les Miserables. The x in exR is a common element in shipping that connect the two names in a pair (e.g. KirkxSpock). e is for Enjolras and R is for Grantaire, a pun off of his name sounding like "big r" in French (grand r). I don't know how you would pronounce it, maybe just as an initialism. I don't personally ship it, but there are strong OTP believers wherever fandoms are found.