What is the ratio of clicks to impressions called?

The metric that shows the ratio of clicks to impressions is called CTR (Click-Through Rate) — the clickability coefficient.

CTR is calculated as:

[ CTR = \frac{Number\ of\ clicks}{Number\ of\ impressions} \times 100% ]

This metric is widely used in advertising and web analytics to evaluate the effectiveness of ads, links, and other interactive elements.