Rustler is a stadium truck. A truggy is a term stolen from the full scale car world that gets misused a lot in the RC car world.
A truggy is a big(tires, lift, etc...), 4WD, big power truck that has been shortened and bobbed and sometimes even boat hulled (it's hard to explain look it up on google). They are designed for extreme off roading and are excellent rock crawlers and mudders. I personally I have never seen an RC that is called a "truggy" that actually is like a real world truggy!
In fact, I don't think I've ever seen an RC "truggy" that is even 4WD!