Crowd
A crowd likely indicates a collective attitude. It is difficult to be oneself in a crowd, to think and move freely; if the crowd moves in a certain direction, it is almost impossible to go in another direction. One is somewhat trapped in the collective and may need to find one's own place for thoughts and creativity. The crowd poses a threat to individuation, according to Jungian analyst and author Robert A. Johnson ("Dream Work").
Collective Level
"Being in a crowd is being in a collective situation... and being at a collective level means being below, since differentiation is always considered to occur above the mass," says Jung in Visions (p. 59), and continues: "[The] general collective level is always several hundred years behind consciousness is another important fact. ... To go down to the collective level always means to go back in time."
Collective Opinions
As a dream image, the crowd can express collective opinions, which react negatively to the dream ego's individuality. For the collective, it is important that one is not "anything other than," or that what the dream ego finds valuable is actually worthless. We always have, to a greater or lesser extent, a conflict within us between being one of many, like everyone else, and expressing our individuality.
Collective Problems
Groups of people often refer to general problems, not individual ones. When dreaming of a gathering of people—soldiers, an audience, a party, and so on—it means that one either is the collective problem or facing it; one is preoccupied with a problem that is not necessarily personal. For example, if one dreams of choosing sides in a conflict between two groups, one is making others' problems one’s own—a situation one could just as easily leave behind.
Common People
But the dream can also indicate that the individualistic person may need to "mix with common people," depending on how the dream unfolds and the dreamer's attitude. (Cf. Bus, Multiple, and Audience.)
Absence of a Crowd
If one arrives at a place that is usually lively with many people, such as a square or nowadays perhaps more commonly a mall, and finds it empty in a dream, it indicates that "the libido has withdrawn"—the place is empty and lifeless; the energy is elsewhere.