They say say that breakfast is the most important meal of the day, but what does it mean? The word "breakfast" actually comes from two words, "break" and "fast". Fast is when a person doesn't eat for a long time. The word is often used by religious people. For example, before Easter many Christians don't eat meat on Fridays, so they say that they "fast" on Fridays.
When people sleep, they don't eat, so this can be called a fast. When a person wakes up and breaks his period of not eating, he breaks his fast. This becomes "breakfast".
※When fast refers to the period of time that one does not eat, it can be a noun 名詞.
例文：His fast lasted for three days.
※Fast can also be used as a verb動詞.
例文：He fasted for three days.