A talented individual responsible for the design and creation of all man-made objects in the known universe, as opposed to a scientist who attempts to make new discoveries about the universe. Engineers do not do much in the way of manual labour; those tasks are allocated to skilled tradesmen. Engineers are involved in the design of everything from oil tankers to staple removers.
For example, a scientist in a lab may discover a new metal with certain properties. An engineer would then take this material, incorporate it into a design, where a welder would then implement it into the machine/device.
Society depends on engineers with their lives just as much as they depend on medical professionals. It is the responsibilty of an engineer to make sure a bridge will stay up, a car will drive straight, and that planes will remain airborne.
Engineering is broken down into many streams. Mechanical engineers would be involved with things in motion, such as a car, or jackhammer. A civil engineer would design bridges and buildings, and other static structures. There are many more streams, which I will not list here.
Often, people without any engineering credentials will append the word "engineer" to their job title. This is because there is a sense of importance attached to the word. Practising engineering without proper certification can get a person sued by a lot of people very quickly.
Engineering is also a term used to describe an action that is similar in nature to engineering, albeit in a non-professional manner. An example of this would be a "social engineer," which is a person that would do something like use a friend's computer to MSN
another friend, and start insulting themselves in order to see what that person will say about them.