Fries means Frisian; from Friesland. The word is used as a noun to indicate a person from Friesland, or as an adjective for all things Frisian.
For research in Friesland, try AlleFriezen, a website with many indexes and scans of Friesland records.
BTW, in English, “Frisian” is used as the general adjective for Fries, while “Friesian” is used for the horses. So don’t call someone a Friesian unless it’s a horse.
Would the surname de Vries be the same as this or a different meaning?
That means “the Frisian,” yes.
Interesting – deVries is my maiden name and I didn’t know its meaning!