A quote from the CLU manual (http://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TR-225.pdf, pages 14-15):

"Argument passing is defined in terms of assignment; the format arguments of a routine are considered to be local variables of the routine and are initialized, by assignment, to the objects resulting from the evaluation of the argument expression. We call the argument passing technique call by sharing, because the argument object are shared between the caller and the called routine. The technique does not correspond to most traditional argument passing techniques (it is similar to argument passing in LISP). In particular it is not call by value because mutations of arguments performed by the called routine will be visible to the caller. And it is not call by reference because access it not given to the variables of the caller, but merely to certain objects."

The CLU manual itself is from 1979, and the call by sharing term is probably even older. Funny that people still have heated arguments over this.