إما لفظاً كقولنا: مسلمون، ومشركون
Or through verbal form, as in “Muslimūn” and “Mushrikūn.”
These expressions visibly take plural forms and denote groups of people. The plurality is apparent in the word's morphology.
In a complete legal context, definiteness, indefiniteness, and other qualifications can affect the reach of a plural expression. The introductory point here is simply that some expressions display plurality directly in their verbal form.