Numeric values, plus optional breakdown metadata, collected direct from source in a format usually dictated by the capabilities of the source data or API. Collected regularly throughout the day with a resolution of up to every 10 minutes, with every 3 or 4 hours being typical. On any given day there can be multiple time stamped values collected.
A KPI can be
a direct daily aggregate of a single data source (a single KPI), or
calculated from a user supplied formula that combines several KPIs, or
a higher level KPI that builds on other existing KPIs that could be from other sources
KPI values are daily but can be recalculated throughout the day as fresh data is collected. There is only ever one KPI value per day.