Cardinality
In plain terms
The number of unique values in a data dimension.
Going deeper
Cardinality measures how many distinct values a field has; high cardinality (like user IDs) strains metrics systems. It affects storage and query cost.
Under the hood
High-cardinality labels in time-series databases explode storage and slow queries, a key observability concern.
Examples
Metric labels, database indexes, time-series, query performance, tagging.
Think of it like...
Like how many unique names are in a guestbook, more names, more to track.