It is just an option to enter a more descriptive name for users instead of showing the column name. The name will be shown instead of the actual column name.
E.g. you can have a setup like this:
Column name: “UserBirthday” <— What you use in your formulas
Long name: “Your birthday” <— What the user sees
Description: “Data will be used to send out birthday discounts” <— What the user sees
If not used, the user will see the normal column name instead.