I'm reading "The Military Institutions of the Romans" by Flavius Renatus, and he states that "though after the example of the Goths, the Alans and the Huns, we have made some improvements in the arms of the cavalry".
I know who the Huns and the Alans are, but searching for more information about the goths was fruitless, and just led me to heavy metal songs. Can anyone explain to me who and what they were? Thank you for your help.
The Goths were a Germanic confederation, most (in)famous for crushing the Roman army at the Battle Adrianople in 378 and killing the emperor Valens, and sacking Rome in 410 (led by their king, Alaric I). Yes, the various other "goths" make finding information harder. You can filter out most of that fluff by searching for "Visigoths" and "Ostrogoths", i.e., the Western Goths and Eastern Goths.
Your question has been asked before. You could start with the respose by /u/shlin28 in https://www.reddit.com/r/AskHistorians/comments/5wpwe1/ancient_goths_what_was_their_whole_deal/
For a book for further reading, my recommendation is Kulokowski, Michael (2006). Rome's Gothic Wars: From the Third Century to Alaric. Cambridge University Press, https://books.google.com/books?id=QXM9SH4EALgC