Rate --> A ratio that compares two quantities with different kinds of rates
Unit Rate --> A rate that has a denominator of 1 unit, a simplified version of a rate
Rate of Change --> A rate that describes how one quantity changes in relation to another
The top example is a Rate while the bottom example is a Unit Rate. Note how it's a comparison between two different quantities (in this case, characters and seconds)
Rates will usually be written with the smaller of the two numbers in the denominator position. This makes it easier to simplify down to a unit rate.