I get so annoyed about this. Especially when it is taught incorrectly in schools

I've just been checking an educational document, and it's full of errors on this subject

In summary:

Mass is measured in kg, and is a measure of the amount of stuff in an object.

Weight in N (Newtons) is a measure of the force acting on an object due to gravity.

So an object can be a 1kg mass, what weighs 9.8N.

It does not weigh 1kg

1kg of sugar is 1kg of sugar on Earth and on the Moon, but the weight on the Moon will be much less than on Earth.

For more info see this:

Mass and Weight
Weight and mass - the difference
http://www.engineeringtoolbox.com/mass-weight-d_589.html

Rant over

I suspect most people probably don't know this.
In the Imperial system, mass is measured in slugs, acceleration in fts^2, and weight in lb (pounds).

So in the two system:

mass = slugs or kg
weight = lb or N

Oh, and here's a cartoon version

http://www.mathsisfun.com/measure/weight-mass.html