A brush truck is a truck that is a combination of an all-terrain vehicle, mini-pumper, and a wilderness rescue vehicle and is used most often to fight wildfires. They usually have a 200+ gallon tank, Indian tanks, chainsaws, picks, fire rakes, and stretchers for rescue operations.
The primary role of this type of truck is to get in where main apparatuses can't, like in narrow roads, fields, or very swampy areas. They can be very useful vehicles. Here is what they look like:
There are other similar fire vehicles that can be helpful, but this one fits into the nooks and crannies that others can't.