The scrum master is the team role responsible for ensuring the team lives agile values and principles and follows the processes and practices that the team agreed they would use.
I found this survey results very interesting.
I found very interesting that, according to the survey, Scrum masters spend less than 12 hours per week on purely "Scrum activities".
Also, most of this time is not in meetings, but on training or refining the backlog.
Typically a Scrum Master does not have any actual authority. This is why becoming an effective Scrum Master is actually very difficult.
read more via Dzone and Scrum Alliance