As a noun, reserve refers to the quality of a shy or modest person who doesn’t easily express his or her feelings. As a verb, to reserve is to stash something away or to set it aside for future use.
Reserve can also refer to backup supplies or resources. If a military is running out of ammunition or food, they may have to dig into the reserve to replenish their supplies. Reserve is also used as a verb to mean "obtain in advance." If you’re expecting a big crowd at your sister's dance recital, you might show up early to reserve seats for your family members. You could also reserve a table at a restaurant for dinner after the show.