It is when a person leans forward as they walk and takes very short fast steps, getting faster and faster until they either stop or fall. My husband used to festinate and fall. He grabbed a lot of mailboxes, telephone poles, and me in order to stop. Now he will not walk outdoors by himself. I pay attention to his posture, and when he starts to hunch over and take shorter steps, I will tell him to stop, straighten up, and start over. Working on walking heel-toe instead of on your toes also helps.