can you give us any references or citations to differentiate the two and clarify what precisely you are talking about i'm finding it difficult to find any reference to straight two at all except those referencing the wikipedia on the other hand i can find plenty that use parallel twin for or degree twins and referred to it as most commonly known if you read the references i gave you will also see it is widely used for automobiles snowmobiles atv jet skis and so on and has been for decades even if you cannot provide references i'd genuinely like to know where and from when the term was used what i think you are suggesting is that parallel twin is used only for degree engines but that is just not so