Duration: How long the cam holds the valves open measured in degrees of crankshaft rotation (cam rotates at half the speed of the crank). Holding the valves open longer allow more fuel and air to enter the engine and exit the engine. Generally, a higher duration number improves top-end power but will sacrifice low-end torque while a lower duration number improves low-end torque but limits the top-end power.
Lift: How far the valve is opened off it's seat; usually measured in inches. Generally, more lift will increase power if the duration is not changed. Any time lift is increased, piston to valve clearance and valve spring coil bind should be checked.
Overlap: The number of degrees that the intake and exhaust valves are open at the same time. Overlap greatly affects idle and off-idle quality. Increasing duration or decreasing lobe seperation causes an increase in overlap.
Lobe Centerline: Highest point of a cam lobe expressed in crankshaft degrees. Usually the average of the opening and closing angles.
Lobe Seperation Angle: Relationship between the centerlines of the intake and exhaust lobes - the angle between the centerlines of intake and exhaust lobes expressed in camshaft degrees. Reducing the lobe seperation angle causes the intake valve to close sooner which results in a gain of low-end power. Increasing the lobe seperation angle causes the intake valve to close later which results in a gain of top-end power.
More terms:
http://www.webcamshafts.com/index_blank.html?pages/cam_glossary.html
More on camshaft design:
http://www.tildentechnologies.com/index.html