This guide will help you understand the difference between terms "Distinct" and "Unique" when working in PowerBI or PowerQuery.
Examples below are in PowerQuery.
Quick look
Distinct: How many different values exists.
Unique: How many values appear only once.
Example below: In "Order ID" field notice 482 Distinct and 221 Unique values. That means that Out of all rows (in this instance 1000 rows), there are 482 (distinct) different values, out of which 221 (unique) never repeat.