What Rating Makes You a "Master"?
The word "master" in chess has a specific meaning: it is a title awarded at a defined rating threshold. The most common answer is 2200 Elo, but the details depend on which federation you are asking.
FIDE system
2200 FIDE = Candidate Master (CM). 2300 FIDE = FIDE Master (FM). 2400 FIDE = International Master (IM). 2500 FIDE = Grandmaster (GM). When most people say "master", they mean 2200+ FIDE.
USCF system
The US Chess Federation has its own titles: 2000 USCF = Expert. 2200 USCF = National Master (NM). 2400 USCF = Senior Master. USCF ratings tend to be slightly higher than FIDE ratings.
How hard is 2200?
Reaching 2200 FIDE puts you in approximately the top 3% of all rated chess players worldwide. Most players who reach this level have studied chess seriously for 5-15 years and play in regular tournaments. See reaching 2000 Elo for a roadmap that gets you close.