Someone who has control, authority, or ownership over something or someone. The term "master" is used to indicate someone of high rank. "Mistress" is the female equivalent of "master." A master can be:
someone who owns an animal or property (Isaiah 1:3)
someone in charge of a household (Mark 13:35)
someone who owns servants or slaves (Genesis 16:9; 39:3; Ephesians 6:5)
an employer (Luke 16:3)
a teacher (Luke 9:49; compare Mark 9:38, which uses "teacher" instead of "master")
the Lord God (Ephesians 6:9)
The word "master" is often used to describe Jesus. When the Greek word kurios (usually translated as "Lord") refers to Jesus, it emphasizes both the authority God gave him and his role in the lives of believers.