A group of geese can have several different names, depending on the physical location or activity of the group. These names include "flock," "gaggle" and "skein."
A flock of geese is a generic term that describes a group of geese that is in any physical location. A gaggle of geese describes a flock of geese that is located on the ground or in any body of water. A skein of geese describes a flock of geese as they fly through the air.
Geese are part of a larger family of animals called the Anatidae, which also includes ducks and swans.