Scrum is an Agile work management method that promotes agility by performing work in short iterations called Sprints. For more on this topic, see Agile and Scrum. This is combined with excellent customer communication and close-knit team collaboration with customers to embrace changes. Scrum can be used for business, IT or combined business and IT projects.
In most enterprises, the coach is the Scrum Master and he/she coaches the team, product owner and stakeholders. To attain the next level requires greater expertise and experience and a Scrum Master Coach will help Scrum teams, Scrum Product Owners and Scrum Masters improve faster and further.
The product owner is the person responsible for product vision and delivering business value with the product. This is managed through a product backlog,which consists of user stories describing what solution features a user wants and what business benefit is delivered by each feature.
The Scrum team is self organizing and autonomous. The team takes the product backlog and estimate the amount of work needed in sprint planning, using planning poker. The team negotiates with the product owner and commits to create particular features in a sprint (this is a design-develop-test iteration time box).
The team works in a daily rhythm within a fixed time box to deliver 'done' product (high quality product meeting customer needs). At the end of the sprint, the team demonstrates the product and explains what was 'done' in a sprint review. The team then reviews the way it worked in a sprint retrospective to list impediments to better performance and selects a improvements to make. The team is then ready to plan the next sprint.
Performance is measured by velocity. This is the number of user stories completed and their story points.
The Scrum Master helps ensure things happen and any impediments are removed to optimize the conditions for team velocity.
The Scrum Guide provides the master description.