The term "relative" has several meanings, depending on its context.
In a general sense, it refers to someone who is related by blood or marriage to another person. This could include family members such as parents, siblings, cousins, aunts and uncles, grandparents, etc., as well as spouses and in-laws.
The term can also be used more broadly to refer to any relationship between two things that are connected or comparable in some way. For example, the relative strength of different types of exercise could be compared, or the relative merits of different job offers could be weighed.
In mathematics and physics, "relative" refers specifically to a vector that represents the difference between two vectors. This can help determine how much one thing changes based on another, such as the velocity of an object changing over time.