A UTM parameter is a tag added to a link's URL identifying exactly which campaign drove that visit.

An upsell email encourages a customer to choose a higher-tier version of something they're already buying.

Unsubscribe rate measures the percentage of recipients who opted out of future email following a specific send.

Unique clicks and unique opens count each recipient once, no matter how many times they engaged.

An unengaged segment groups contacts by multiple weak engagement signals combined, not a single inactivity flag alone.

A target audience is the specific group a particular campaign or message is built for, narrower than a market segment.