a crowd: a large, loosely-gathered body of ordinary people
At its core this word names a mass of people who happen to be together, not an organized assembly. It is the throng that gathers around Jesus to listen, to be healed, or simply to see what is happening, and it is by far the most common word the Gospels use for the people who fill the scenes of his ministry.
The same word stretches in two natural directions. Because such a gathering is made up of regular people rather than officials, it slides easily into meaning the common people, the populace set over against the rulers and the educated few. And because a large unorganized crowd is easily stirred, it can shade toward an unruly mob, especially in Acts where crowds are roused to riot.
These are not separate words but one picture seen from different angles: a body of ordinary people, sometimes simply present and listening, sometimes named as the populace, sometimes churned into a mob. A few times the picture widens past any single place to mean a vast multitude, a sheer number too great to count.