A KPI is a number chosen because it tells you how something important is going. It should be clearly defined, measured the same way each time, and compared with a target or with its own past performance, otherwise it is just a statistic.
A transport firm might watch on-time delivery and cost per mile; a retailer might watch sales per site and stock turnover. Fewer is better: a handful of KPIs that people understand and act on beat a wall of charts. They are most reliable when drawn straight from the system where the work is recorded.