One major difference between a master's degree and a Ph.D. is the level of learning required. You can typically find both a master's degree and a Ph.D. in almost all subjects, but the Ph.D. represents a greater level of learning. Students will have taken more classes to get a Ph.D., and will have completed more in-depth studies to do so than for a master's.
The time needed to complete each degree also is one major difference. Typically, a master's degree takes between 2 and 4 years, and a doctorate degree or, Ph.D., can take between 4 and 8 years to complete. Typically a Ph.D. also includes some type of work at the end of the degree program, such as being a medical resident, or teaching for a couple of years in a program you study. This tacks time on the end and is another difference.
Many Ph.D. degrees are thought of as "terminal" degrees, meaning that once a person gets one, he is finished with school, unless he decides to pursue a different topic. However, master's degrees are often seen as a steppingstone between a bachelor's degree and a Ph.D. Many people who obtain a Master's degree then go on to get a Ph.D. in the same or a related field.
Usually, a Ph.D. requires a committed move on your part, because not every school or college will have a Ph.D. program in every subject. However, master's degrees are becoming more common, and are more likely to be seen in campus programs at colleges, or in nontraditional programs like online learning.