Sentence:  A <WSD>semidirect</WSD> product is so called because a direct product "G" of "K" and "Q" requires, in addition to "K" + "Q" = "G" and "K" ∩ "Q" = {1}, that both subgroups "K" and "Q" be normal (Proposition 1.86); here, only one subgroup must be normal. 
Meaning of the word marked with <WSD> tags:  That has the nature of, or has a nature that derives from or is analogous to, a semidirect product.