The term 'Half a Tetrad' refers to a DYAD, which is a pair or group of two people or things. A DYAD is a type of relationship between two people or things that are connected in some way. It is often used to describe the relationship between two people who are in a romantic relationship, or two people who are working together on a project. A DYAD can also be used to describe the relationship between two objects, such as two pieces of furniture or two pieces of clothing.