Rate is a special kind of ratio, or relationship, between two measurements. There are many different types of rates: for instance, pay rate (dollars per hour), and heart rate (heartbeats per minute). When you see the word “per,” you’re usually talking about a rate.
Another type of rate is speed, the relationship between distance and time. When we say we’re driving 10 miles per hour, we mean: for every hour (time), we cover 10 miles (distance).