Adsense CTR & CPC

CTR = Click Through Rate as a %, divide the # of clicks by the # of page views or # of ad impressionsCPC = Cost Per Click as an average of what you are getting for each click, so it's total earnings divided by # of clicks
RPM = Rate Per 1000 Impressions, is just a reference # of what you are currently earning (or would be earning) for every 1000 impressions and not what you are actually earning or will be paid.. Take total earnings divided by # of page views or ad impressions multiplied by 1000. So whether you are actually getting 1000 impressions or not doesn't matter.
For More Info: Clickthrough rate (CTR) - AdWords Help

Nature Facebook Covers

CTR - The click-through rate of an advertisement is defined as the
number of clicks on an ad divided by the number of times the ad is
shown (impressions), expressed as a percentage.
For example, if a banner ad is delivered 100 times
(100 impressions) and receives one click, then the click-through rate
for the advertisement would be 1%.

CPC - Pay per click (PPC) (also called cost per click) is an
Internet advertising model used to direct traffic to websites,
where advertisers pay the publisher (typically a website owner)
when the ad is clicked. With search engines, advertisers
typically bid on keyword phrases relevant to their target
market.
Content sites commonly charge a fixed price per click rather
than use a bidding system. PPC "display" advertisements,
also known as "banner" ads, are shown on web sites or
search engine results with related content that have agreed
to show ads. This approach differs from the "pay per
impression" methods used in Facebook, television and
newspaper advertising. Similar to the pay per click model
which often uses a bidding system, with the online pay per
impression method, advertisers bid how much they are
willing to spend for their ad to show up 1000 times.