A socionics small group is the descriptive intersection of 4 different types, or the sum of 3 different dichotomies. It provides a different angle and a more specific systematized understanding of personality differences.
For example: What do LII, LSI, ESI, and EII have in common? Or, equivalently: What does the sum of Introversion, Conscientiousness, and Constancy represent? It's described in the temperamental small group called Balanced-Stable.