Click-through rate (CTR) is the ratio of users who click on a specific link to the number of total users who view a page, email, or advertisement. It is commonly used to measure the success of an online advertising campaign for a particular website as well as the effectiveness of email campaigns.
As an example, the average click-through rate on AdWords paid search ads is about 2%. Accordingly, anything over 2% can be considered an above average CTR. Across all industries, the average CTR for a search ad is 1.91%, and 0.35% for a display ad.