Fixed Blade Knives
A fixed-blade knife will never surprise you in use because it is a solid piece of steel anchored to the handle. For those who want a blade they really trust for tough jobs, such as field dressing and tough camping tasks, a fixed blade is the answer. Fixed blades are durable and hold up to the elements well because of their straight, simple construction without folding mechanisms. In fixed blade knives, the blade is one piece of metal that runs the length of the knife. When the blade reaches the beginning of the handle, it can either taper into a rat-tail that is surrounded by the handle or not taper and continue as a tang that is covered on either side by handle "slabs."
Folding Blade (folder) Knives
Folding blade knives are generally not quite as durable as fixed blade knives, but provide safety and the carrying convenience of compact size. Folding blade knives (also known as a pocket knife) come in a variety of configurations, some of which lock into place. Locking folders allow much of the same confidence of a fixed-blade while letting you close the blade into the handle for safety.
Lockback - Many knife users are looking for the convenience of a knife that provides lock-open safety. A "lockback" knife requires two-handed closing via a mechanism usually located on top of the handle end. Some lockbacks are one-hand opening.
Liner Lock - One-Hand Opening and Closing - A "liner lock" knife enables the user to open and close the knife with one hand. Liner locks (also referred to as a locking liner) also provide lock-open safety. Some liner locks are designed for both right and left-hand use. If your activity leaves you with only one hand free, such as climbing, then this is the type of knife for you.
Pocket Knife - Good, old-fashioned pocket knives are still high on the list of favorites-great to carry in your pocket for all the times you might need a knife. Not all models lock open, but that's not critical for their utilitarian use. Some pocket knives offer multiple blades for different uses.
Much of this information was taken from the Buck Knives company website.