Click-Through Rate 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's used to measure the success of an online advertising campaign for a particular website as well as the effectiveness of email campaigns.

Formula: CTR = (Number of Clicks / Number of Impressions) x 100

Why it's important:

• Indicates the relevance and effectiveness of ads or content
• Helps in optimizing ad campaigns and content strategy
• Can affect Quality Score in paid advertising, influencing ad costs and placement