What is the best classification for individuals milling around in crowds or waiting for a bus?

The best classification for individuals milling around in crowds or waiting for a bus is a social aggregate. A social aggregate refers to a collection of individuals who are in the same place at the same time but do not interact with each other in a meaningful way. They may share physical proximity, such as in a crowd or a bus stop, but this grouping lacks the characteristics of more structured social relationships.

In contrast, a social category would involve individuals who might share a similar trait or characteristic, such as age or occupation, without necessarily being in the same location or interacting. A secondary group is characterized by formal, impersonal interactions and often exists to achieve a specific goal, such as a workplace or a committee, which does not apply to individuals in casual settings like waiting for a bus. Lastly, a primary group consists of close, personal relationships characterized by emotional ties and ongoing interactions, such as family or close friends, which is also not reflective of the situation described.