(5)The definition of infinity is not something we can't find an bondary, but something we can not talk about any quantities outside it and can be defined as the open quantity that can compress anything outside it into nothing,and something we can not reach it by extending forever of finite quantities. Thus, we say that if the superpositions of the infinitesimal constantly extend to close to a certain quantity, the quantity is considered finite , and if the infinitesimal does not constantly extend close to a certain quantity, the quantity is considered infinite., Therefore, infinity is the accumulation of infinitely many finite quantities and is precisely defined as something that goes on forever and never reaches it .