A unit rate simply means how many of one type of units you get per 1 other type of unit.
Examples of that:
\(300\frac{l}{ s }\)
This is rate of fluid flow of some pump for example. It pumps 300 liters every second.
Other example:
\(50 \frac{km}{h}\)
This is example for speed. Somebody is moving at 50 kilometers per hour (every hour he travels 50 kilometers)
