Reading comprehension is how well a person can read and understand a text. Fluency is the measure of how well a person can read a text aloud with feeling.
Reading Comprehension Involves Getting the Facts
A reader with good comprehension will be able to recall specific information that is presented in a text, such as dates, names and the order in which things occurred.
Comprehension Also Involves Getting the "Big Picture"
Comprehension is also about understanding the point of a passage. Consider the introductory paragraph of this article: a reader with good comprehension could not only define reading comprehension and reading fluency, but also explain the difference between them.
Fluency Is a Useful Skill
Comprehension is tested on standardized tests like the ACT. Testing for fluency is not common, but people who read fluently are viewed positively at school, work and other public situations.
Vocabulary Is Important
Both comprehension and fluency depend on knowing the words being read, hence developing vocabulary is an important way to improve these two reading skills.
Comprehension and Fluency Can Be Improved
In addition to developing vocabulary, exposure to reading material that is made increasingly difficult over time will improve these both reading skills. Listening to fluent reading by a good reader also fosters fluency development.