KPI in email marketing means Key Performance Indicator. KPI measures the success of your email campaigns. Open rate shows how many people opened your email. Click-through rate tracks user interaction with links. Conversion rate measures how many took the desired action. Bounce rate identifies emails that failed to reach inboxes. Unsubscribe rate shows user dissatisfaction. Delivery rate measures how many emails were successfully sent. List growth rate tracks the increase in your subscribers. ROI calculates the revenue from your campaigns. Each KPI gives insights into your email performance. You should monitor KPIs to improve your email marketing strategies effectively.