Xform naming in new pull syntax

Why do datomic team choose xform for the “function that transform the value” in datomic?
xform is also used in clojure.core to represent “a function that receives a ‘reducing function’ and returns a 3-sig function”

There is some abstract that describes what is a xform? they are completely unrelated?

It is just short for “transform”. The prefix “trans” means “across”, and an “x” is a cross, so it’s used as the abbreviation sometimes.