Wrong! It should be WHO is a dependent because people are people, not things. Unless you are weird; don’t be weird.
A dependent is anyone who is entitled to claim a dependency exemption. Otherwise known as: money! More specifically, money deducted from the adjusted gross income for the sake and purpose of taxes.
So your dependent is someone (who is not you) who gets money, as dependency exemptions can reduce taxable income, leading to… you guessed it, less income tax.