Unless you are an advertiser or AdSense site builder you might not know what those terms mean, but they are very different. They are highly relevant if you are an advertiser of an online publisher.

With AdSense, for example, you get paid per click, and the cost to the advertiser is therefore cost-per-click. CPM, however, is cost per thousand impressions.

Just to add to the confusion there is CPA or cost per acquisition. So what do these mean to you as a website owner and advertiser? With some advertising programs, you have the choice of paying or being paid, depending which side of the fence you are on, by CPC or CPM.

CPM attractive for high-traffic sites

If your site gets a lot of traffic, and the site is of a general nature, then CPM is attractive. you will get paid every time anyone arrives at the web page. But hold on: although this sounds good, the payments are very low. You need to get quite a few visitors just to earn a dollar.

With CPC you can soon find what you are being paid and whether it is worthwhile. Generally, if you have a niche site, CPC is better because people who click on the pages are interested in what is on offer. Also, by the time they decide to click on the advert, you have lost them. They have decided to move onto somewhere else.

More CPM adverts available for your site

Most of the adverts you can put on your site are paid for on a CPC basis, or on a set fee per month. CPM is not that common. However, Chitika, which places adverts on sites with the same relevance to the content as Google AdSense, has just introduced CPM banner adverts. As I said, if you are getting a lot of traffic, it is worth switching to these CPM banners, at least for a month. This is particularly worthwhile if a high proportion of visitors do not stay on the site for very long.

The good thing about CPC advertising to the publisher is that by altering your keywords you can make your page receptive to adverts that have high payouts. Of course, these keywords must be relevant to the page, but there are many pages where a keyword could be changed without damaging the page. For example, it might be that 'digital photography' earns more per click than 'digital cameras', or vice versa. By finding out the payout for both terms, you could then target your site to suit the higher payout.

It is also worth experimenting with CPM and CPC adverts, whether you are an advertiser or publisher. It is also important that you track the success of all your adverts as well.