A moment is a particular point in time. Some moments you remember forever: like the moment you earned your driver's license or the moment you learned that you passed Organic Chemistry.
A moment is a short, but unspecified, amount of time. At Thanksgiving, you are supposed to take a moment to be grateful for friends and family. Or maybe you have been asked to observe a "moment of silence" for a national tragedy. Moment can also mean "importance." If you say something is "of little moment," then you are saying it doesn't matter.
1 
n 
an indefinitely short time

2 
n 
a turning force produced by an object acting at a distance (or a measure of that force)

3 
n 
the nth moment of a distribution is the expected value of the nth power of the deviations from a fixed value
