The type or membership type field is a free text field. You may type whatever text your need into this field.
At a later date, you may decide to combine two membership types into one. For example, you may have a Family of 5 membership and Family of 6 membership. You may decide to combine these memberships into one Family of 5+.
You may also have typos in a membership type. One employee may add a Family membership and a second employee may add a Familyy membership. You will want to fix the Familyy memberships easily.