From Wikipedia:
Spam's basic ingredients are pork with ham added, salt, water, modified potato starch (as a binder), sugar, and sodium nitrite (as a preservative).
Hormel claims that the meaning of the name "is known by only a small circle of former Hormel Foods executives", but popular beliefs are that the name is an abbreviation of "spiced ham".
https://en.wikipedia.org/wiki/Spam_%28food%29