This is the intended effect of every graphic design. All the elements appear as if they belong together. The graphic has good balance, proportion, and harmony. There are several forms of unity. Thematic unity occurs when all the items are related to one another.
Tonal unity occurs when all the items in the graphic have a consistent look and feel.
Visual unity results when the items have a clear visual relationship and it is in keeping with the message of the graphic. Typographic unity occurs when the style of the typeface is consistent with the message of the graphic.