schoolbag是书包的意思，而backpack则是背包的意思，区别可以从以下例子看出：Where is your school bagThis is a backpack which you should keepit for holiday. You need a school bag for your school. 你的书包在哪里？ 这是一个背包，你应该假期才用。

你去学校需要一个书包。