Base currency
The first currency in a pair: the one whose single unit is being priced.
How to read the number
A rate answers the question of how much of the second currency one unit of the first costs, and that is where the direction of the pair is read.
When the metric lies
Swapping the order of the currencies inverts the meaning: a rise in one form of the pair is a fall in the other, so the phrase that the rate went up says nothing without the pair.
Also known as: first currency in a pair