A relative is a person who is part of your family. Parents, siblings, uncles, aunts, grandparents, cousins, nieces and nephews — they're all relatives.
A relative can be connected to your family through blood or by marriage. If you are a child or grandchild of Maria's, for example, you are a blood relative of her family. If you marry Maria's son, you become a relative by marriage. Relative is also an adjective that means "estimated by comparison," like the steep hill that is tiny, relative to the mountain behind it.