Bodies of collected text taken together as material to study. A corpus is defined by what was gathered, and its edges are a decision.
Latin corpora, plural of corpus (body); bodies of collected text taken together as material, the plural naming that the edges of the collection were someone's decision, not a natural boundary.
It is corpus multiplied, and the plural itself makes a quiet claim: that several bodies of text can be compared as bodies, each with its own drawn edges, without becoming one larger body by being studied together.