What is the primary defining characteristic of an irregular galaxy?

The lack of a coherent structure such as a spiral disk or a distinct elliptical core.

An irregular galaxy is classified by its amorphous and chaotic appearance, which distinguishes it from the highly ordered spirals or ellipses. Unlike galaxies with predictable structures that allow for easy classification into specific morphological groups, these galaxies lack symmetry, defined central bulges, or organized rotation patterns. They appear as disorganized and misshapen clouds of gas and stars, often retaining their chaotic form regardless of the angle from which they are observed.