A dutch oven is an oval or round shaped pot (usually cast iron) with a matching lid and handles on either side. Usually titled "dutch oven", sometimes called "Cocotte" or "French Oven".
A casserole is a dish with high sides and comes with a lid. Casseroles are very similar to Dutch Ovens but side walls usually aren't as high.
A braiser looks like a casserole or a dutch oven, but with a wider and flatter profile, they may or may not have a lid. Many braisers come with a rack insert for cooking meat.
Ply Construction: This type of cookware has multiple layers of metal bonded together on the bottom of the pot or pan (and often times around the vessel itself). The higher the ply count, the thicker the cookware is. This type of cookware provides very uniform heat distribution.
Solid Construction: This is the most common type of cookware. It has a solid metal body, and often comes with a non-stick finish.