Refresher (noun)

1. Something that restores or revitalizes.
2. A course or program that updates or reviews information or skills.

Origin:

From the verb "refresh" which comes from the middle english word "refresshen" meaning "to give new strength".

Examples:

1. The cold water was a refreshing change from the hot sun.
2. The minty gum was a refreshing treat after a heavy meal.
3. The refresher course helped her to brush up on her language skills.
4. The refresher training is required for all employees every two years.
5. The refresher program is designed to help participants stay current in their field.