Can someone clarify the difference in terminology?

Tempo= "In musical terminology, tempo ("time" in Italian; plural: tempi or tempos) is the speed or pace of a given piece. Tempo is a crucial element of most musical compositions, as it can affect the mood and difficulty of a piece." BPM on SP is the tempo.
http://en.wikipedia.org/wiki/Tempo

Pitch= basically the note or frequency of a sound. The term is also used as a verb- to "pitch' a sound or sample would mean to adjust what frequency or note it is. If you have a sample of a C note and you "pitch" it to D you have actually re-tuned the note 1 whole step to D. Many people want to adjust pitch but retain the rate or speed of the speed at which it plays back (for beats etc) and this requires lots of complex/powerful processing power to avoid it sounding bad. This is why most gear like SP don't do this well and computers can do it very well.
http://en.wikipedia.org/wiki/Pitch_(music)

Tune- multiple meanings. Can mean same as Pitch/verb. You can replace the word "pitch" in above description of pitch with word "tune" and is same.
http://en.wikipedia.org/wiki/Tune

C