What's the difference between defamation and slander?

What's the difference between the two?
Why would someone take someone to court for slander or defamation?
I'm asking this cause I just got an idea to take a "friend" whose saying I gave her these gifts and stuff that I didn't give her...but her fiance...who none of her family likes gave it to them.
Could I take her to court because of this? It's making me sooo poed. I can't stand it.

its basically the same thing. unjust injury to the reputation of another.

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It appears that slander has more to do with oral communication whereas defamation includes written communication:

 
slan·der (slan'd?r)
n.

Law. Oral communication of false statements injurious to a person's reputation.
A false and malicious statement or report about someone.

 
def·a·ma·tion (def'?-ma'sh?n)
n.

The act of defaming; calumny.

 
de·fame (di-fam')
tr.v., -famed, -fam·ing, -fames.

To damage the reputation, character, or good name of by slander or libel. See synonyms at malign.
Archaic. To disgrace.

 
li·bel (li'b?l)
n.

A false publication, as in writing, print, signs, or pictures, that damages a person's reputation.
The act of presenting such material to the public.