This is a post from Google blog:
At our Mountain View headquarters, we have some fields that we need to mow occasionally to clear weeds and brush to reduce fire hazard. This spring we decided to take a low-carbon approach: Instead of using noisy mowers that run on gasoline and pollute the air, we've rented some goats from California Grazing to do the job for us (we're not "kidding").
What are brushes mentioned above? I've looked it up in several dictionaries, but couldn't find a definition that makes sense to the context.