KPI stands for Key Performance Indicator.
It is actually the goals you agree to measure with your team and it should be pretty stable during the time.
A typical example of KPI is the visitors to your site. Another common KPI is the sales you achieve through any medium.
More complex KPIs could exist, like marginal costs of new customers, SEO positions for certain KW (keywords), etc
If you want to see how a proper and successful digital marketing strategy is being designed and performed you should Contact Us and book a meeting.