A dyad is a group of two, a tetrad is a group of four; for a group of three you can use the term triad.

The Nucleosome has an approximate two fold axis of symmetry which is called the Dyad Axis. So when you rotate the Nucleosome by 180 degree you would observe the similar view of Nucleosome before the rotation.

A dyad in sociology refers to a social group of two individuals. In a dyad, the relationship dynamics are more intense and personal compared to larger groups. An example of a dyad is a close friendship between two people.

A dyad family is a family composing only of a husband and a wife without children.

Dyad is a conversation face to face between two persons particularly, but may include others.