What defines the primary structural difference between open clusters and globular clusters?

Answer

Open clusters are loose and irregular while globular clusters are dense and spherical

Open clusters are characterized by a sparse, irregular distribution of a few hundred to a few thousand stars, lacking centralized density. Conversely, globular clusters are massive, tightly packed, spherical systems containing hundreds of thousands or even millions of stars held together by intense gravity. This difference in physical organization makes open clusters appear spread out and globular clusters appear as dense, fuzzy balls of light.

What defines the primary structural difference between open clusters and globular clusters?
clusterstarObjectaggregation