A course that reviews and updates a topic for those who have not kept abreast of developments(noun)
WordNet. Princeton University. 2010.
Use "refresher course" in a sentence
""Thank God Maria gave me a refresher course on Viking art last night."
"Standing at the back of outdoor rallies, clad in a bulky anorak and bobble cap while she attended a weekend refresher course on whatever it was she needed to refresh."
"He talked it over with his second-in-command and platoon commanders while, from different parts of the company locality could be heard NCOs putting men through their paces - Master Corporal Fred Terry practising with his Number 2 on the Carl Gustav MAW; Private John Grimes undergoing a local refresher course in stoppage drill on the 113's 50-cal gun."