Peter Johnstone asks who coined the term "pushout". On page 156 of Abelian Categories I wrote (43 years ago!): The word "pullback" and the ubiquity of the concept I learned from Lang, who also pointed out the pullback theorem and its importance. I plead guilty to "pushout"... (www.tac.mta.ca/tac/reprints/articles/3/tr3abs.html) MathSciNet lists Alex Heller's review of Abelian Categories as its second oldest use of the term "pullback" and its oldest use of "pushout". (Its first use of "pullback" is in Alex's review of John Gray's 1962 paper "Category-valued sheaves" -- no the stalks were not categoies.) It was my impression that Serge Lang invented the term "pullback" (his term for the dual notion was "co-pullback"). Note that I refrained from stating this impression. But I do claim to have invented the term "pushout" -- indeed, I've been know to cite this as my most visible contribution to mathematics.