Click-through rate
Click-through rate or CTR is a way of measuring the success of an online advertising campaign. A CTR is obtained by dividing the number of users who clicked on an ad on a web page by the number of times the ad was delivered (impressions). For example, if your banner ad was delivered 100 times (impressions delivered) and 1 person clicked on it (clicks recorded), then the resulting CTR would be 1%.
Banner ad click-through rates have fallen over time, often measuring significantly less than 1%. By selecting an appropriate advertising site with high affinity (e.g. a movie magazine for a movie advertisement), the same banner can achieve a substantially higher click-through rate. Personalized ads, unusual formats, and more obtrusive ads typically have higher click-through rates than standard banner ads.
References:
Sherman, Lee and John Deighton, (2001), "Banner advertising: Measuring effectiveness and optimizing placement," Journal of Interactive Marketing, Spring, Vol. 15, Iss. 2.