Simple Definition:

A relationship is a connection or bond between two or more people [individuals]. It involves how these people [individuals] interact, communicate, and feel about each other. Relationships can be romantic, such as a marriage or dating, or they can be platonic [non-romantic], like a friendship or a professional relationship. For example, a romantic relationship can involve a couple who love and support each other, while a friendship involves two people who enjoy spending time together and being there for each other.

Very Simple Definition:

A relationship is how people connect with each other and feel about each other. It can be between friends or people who love each other. For example, friends play together and help each other.