Drive is a service from Google which allows you to store, access, and collaborate on files in the Cloud. The 'Cloud' is a term which means that your files are stored online, rather than on the hard drive of your computer (or a USB thumbdrive). This means that you don't need to worry about backing up files, remembering your USB drive, or students not being able to complete homework at home. Drive means that no matter where you are, your files are there with you. This video outlines some of the advantages of using Drive in Google Apps for Education.