A Dependant is a person who relies on you to support their main source of living. In general, anyone you claim on your income tax return is considered a dependent. For example, a minor child that you have custody or a spouse that financially depends on you. A child can be biological, legally adopted or a step child. However, you may exclude any unmarried children under 21 years of age, if these children have reached majority under the law of their place of domicile.
Non-family member can also be dependents. Even if you are not legally obligated to support that person or you are not related.