Terms work in a way which is similar to Schedule Tags. You define Terms in the Calendar tab of the admin console.
Terms can overlap. So you can have one Term tag for each Quarter, each semester and the Full Year and they can all be used together.
When a Schedule Entry contains a specific term Tag, it will appear to users only during that time. If you wish the section to appear during multiple Terms, you can either create a single term which encompasses the whole period, or have two entries, one for each term. This will vary based on the way your SIS defines their own schedules.
To apply a Term tag to a schedule entry, pick the correct one next to each entry. EVERY entry MUST have a term tag as soon as they exist. If not, that schedule entry will not find the tag on the given day and thus not add itself to that day.