Scrum is an agile framework for developing software but can be used in many other industries as well. Scrum was created by Jeff Sutherland and Ken Schwaber in early 1990s and has since been the most popular agile method.
Scrum of Scrums is a technique to scale up Scrum in larger groups and scaling the daily Scrum. Scrums of Scrums is not part of the Scrum guidelines but can be used as a complementary when scaling to more than one scrum team.
The purpose of a demo is to present and review the work of a team or teams. After an iteration of work the demo, usually, naturally ends the period and the teams can show whats been done.
Retrospective is a planed time, usually a meting or workshop where the team can start to reflect over the work that´s been done the last period. Retrospective is where the team can analyse, examine and look for improvements in their work process and also a great way to learn from each other.
Timebox is a method when work is divided in smaller and separate time slots.