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/Peo, FreeWebSpace.net
cpm - cost per mille (i think its millie could be wrong)
Its the cost to an advertisng for you showing 1000 banners impressions of there banner, this may be non unique or unique usually non unique for banners but for pop ups its usually based on a 12 - 245 hour uniques.
cpc - cost per click
You don't get paid for showingt he ad unless someone clicks on the ad, this is most unfair system as it relies ont he banners being made clickabale, Most banners are made to get the lowest ctr ever, like dell adverts on valueclick, I see them all over but would never click one unless by accident.
I think czar has a little list he posts to people who ask this very question that will probably explain them better than I could.