First let me say that, as frugal as I am, the long skinny butcher knife shown on the "butcher block" table in that good photo above looks EXACTLY like the one I was using when I was just a kid in my early teens. I tried to chop a very small scrub oak (about 1.5 inches in diameter) and promply WRINKLED THE EDGE. It was too soft and thin for chopping, as I learned at that time! Slicing yes, chopping no! Live and learn, die and forget it all, as Mr. Moxley often remarked. (He also said "DO SOMETHING, even if it's wrong!)
As has been said many times, a "survival knife" is the one in your pocket or on your belt when the SHTF, your world is quickly turning to stinky, fresh fertilizer, and you need to bail of there immediately if not sooner! The moral to that story is to never leave home without at least one good knife you know you can depend on in your pocket or otherwise on your person. Cost of said knife need not be a serious factor, though. Personally, I strongly favor a Victorinox SAK of the Farmer, Pioneer, or Soldier variety, though preferably one with a saw blade along with the the other SAK basics (BASICS!) and the stronger aluminum handle scales. But I'm never without at least 2 or 3 folders on my anytime I have pants on, and a SAK is ALWAYS one of them!
But the answer to the question, "What is a survival knife?" is determined by what you need to survive, where you are in a jam, and how long you might be there before help can find you or you can find help. If you can walk away after your plane goes down in Central or South America you better pray you have a decent machete with you, even if the blade is only 12 inches long. (Hey, gringo, habla machete? Si, muy bueno!) On the other hand, if you found yourself in the Canadian woods and hoping to find your way out to a road, then that Falkniven mentioned earlier, or another simple belt knife with a blade about 4 to 5 inches long would be more appropriate probably.
Obviously, the more complete your tool kit is, the better you can adapt to the situation you have to deal with and the better your chances of surviving your problem long enough to get back to where the cold beer stays. With enough skill and cunning, you might get along just fine with some kind of standard pocketknife. But if you could add some kind of big knife (machete, Bowie, kukri, etc.) you would be much better off. Now if you could add a small belt knife to those two you would be even better off. And if you could add a tomahawk, hatchet, or light axe you would be better off still. Now add your favorite pliers-knife multi-tool and you would have a very complete tool kit. It's just a matter of what you are willing to carry or keep very near you at all times. Most of us find a compromise toward the simple end of the scale under normal conditions. Your additional equipment can stay in your bug out bag usually.