A scrum is an iterative, incremental process for developing software in chaotic environments. Scrum consists of a series of 30 day sprints, each sprint producing an executable. Between sprints, all interested parties evaluate progress and reevaluate technical and business requirements. Work is reestablished and the team enters into another sprint. There are other agile methodologies that rely on a 14 day sprint or up to a 90 day sprint.
The scrum master holds the daily scrum meeting to make sure everyone is unblocked, check progress, and determine what is preventing more progress. It is a short meeting, never more than 30 minutes, and is restricted to getting commitments for the next day, and what has blocked commitment for the previous.
Followup meetings can be scheduled to deal with the issues identified, and these have of course can use another meeting style. An advantage of immediate followup is that everyone required for it has just come out of the scrum, and so is available immediately.
It is basic to the scrum process that everyone be available for that 30 minute meeting. It is not clear how well these methods work with telework or any very distributed project.
The Scrum Alliance certifies their "scrum masters" as being able to conduct these meetings the right way.