Out of those options, I would choose the third - nothing about good/bad, just a location.
"The Strip" is the southern part of Las Vegas Boulevard; over the past couple of decades or so, it has grown further and further south, so that now it extends several miles outside the actual city limit. If you are arriving from the airport or via highway from Los Angeles, the Strip is the first thing you see (and it can be hard to remember that there's anything else there at all!)
I don't have hard data for this, but I would guess that over 90% of visitors to Vegas never leave the Strip; this means that real estate just off the Strip is much cheaper, but that off-Strip business owners must either work much harder to bring in the tourist crowd, or concentrate on building a clientele among local residents. Off-Strip restaurants, therefore, tend to be much like local restaurants everywhere else; if you go to Vegas expecting to eat at a celebrity chef's restaurant, you'll have to stay on-Strip.
There certainly are some sketchy neighborhoods in Vegas (or just outside it), but they tend to be several miles from the Strip; generally the term "off-Strip" means just off the Strip, rather than far away from it.