A gaggle is a group of geese. You can also describe a bunch of people milling around in a disorganized way as a gaggle.
Gaggle is a word known as a "term of venery," a collective noun used to describe a particular group of animals. When a bunch of geese waddle around on the ground, that's a gaggle of geese. If those same geese were flying overhead, you'd call them a flock or a skein instead. Gaggle is also useful for describing a disorderly or chaotic group of people: "I was surrounded by a gaggle of three-year-olds eager to pet my puppy."