The rake is an item that is found in The Garden. It is the focus of the fifth mission, Rake in the Lake, which tasks the Untitled Goose with stealing it from the shed and placing it in the lake.
However, the rake is easy for The Groundskeeper to notice being stolen, and if so, he will chase the goose off. To safely get it in the lake, the player must cause another problem for the Groundskeeper to fix, causing him to be too focused on the task at hand to notice the rake being stolen.