A gesture is an inventory item that allows a user to do a task of things from one command (similar to a "macro"). For example, a user could create a gesture that plays an animation that makes their avatar say "Hello!" when the user types "/hello". Sounds, animations, and text can all be "cued" by a gesture. Only one gesture can be cued per line of chat and each gesture can only have 20 "steps".
Create a gesture by using the gesture window. To open the gesture window either right-click the avatar and select "Gestures" from the pie menu, or select "Gestures..." from the edit menu, or use the keyboard shortcut "Ctrl-G".
Edit a gesture by opening the inventory, going to the "Gesture" folder, and double-clicking the desired gesture to edit.