Need clarifications on some terms related to AD

3
I Need to know about the terms related to AD's.
CTR
CPI
CPM
CPC
CPA

And other rating (if any exists) on which money is given to an ad.
CPC - Cost per Click

You will get earning per click..


CPM or CPI- Cost per Thousand Impression


You will get amount per thousand ad views.


CTR - Click Through Rate


CTR = CPC divided by CPM

Here is some more :

CPS - Cost Per Sale

CPL or CPA - Cost Per Lead (Forum Filling on Advertiser site)

Pay Per Call - Paid for every call placed to a customer care.
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Which is best ?CPC, CPM or CTR ?

    Need clarifications on some terms related to AD