Click Through Rate

I just learned a new term,
click through rate.
I learned it on this Adwords
help page:

How do I know
if my ads are
running and performing well?

It sounds like click through
rate is a key concept. If I
understand correctly, it is based
on the number of ad impressions.

Here's my understanding. Let's
say you ad had appeared 1,000
times. One thousand is the number
of ad impressions. The appearance
of your ad is an impression.

Let's also say that 10 people click
on your ad. Now you have all the
data you need to figure out your
click through rate. Click through
rate is the number of times users
have clicked on your ad over the
number of times your ad has been
displayed.

Expressed as a fraction, click through
rate looks like this:

clicks / impressions

Click through rate is expressed as a
percentage. Therefore, a click through
rate of one percent on one thousand
impressions is ten clicks.

Here's a simpler way to look at it:

Everytime your ad displays it is an
impression. Just because you made an
impression does not mean you got a click.

If you get 10 clicks for every 1,000
impressions you make, your click through
rate is one percent.

Ed Abbott