Scrum (development)

Scrum is an iterative, incremental framework for project management and agile software development.Although Scrum was intended for management of software development projects, it can be used to run software maintenance teams, or as a general project/program management approach.

Characteristics
Scrum is a process skeleton which contains sets of practices and predefined roles. The main roles in Scrum are:
the “ScrumMaster”, who maintains the processes (typically in lieu of a project manager)
the “Product Owner”, who represents the stakeholders and the business
the “Team”, a cross-functional group of about 7 people who do the actual analysis, design, implementation, testing, etc.
During each “sprint”, typically a two to four week period (with the length being decided by the team), the team creates a potentially shippable product increment (for example, working and tested software). The set of features that go into a sprint come from the product “backlog”, which is a prioritized set of high level requirements of work to be done. Which backlog items go into the sprint is determined during the sprint planning meeting. During this meeting, the Product Owner informs the team of the items in the product backlog that he or she wants completed. The team then determines how much of this they can commit to complete during the next sprint.During a sprint, no one is allowed to change the sprint backlog, which means that the requirements are frozen for that sprint. After a sprint is completed, the team demonstrates how to use the software.
Scrum enables the creation of self-organizing teams by encouraging co-location of all team members, and verbal communication across all team members and disciplines that are involved in the project.
A key principle of Scrum is its recognition that during a project the customers can change their minds about what they want and need (often called requirements churn), and that unpredicted challenges cannot be easily addressed in a traditional predictive or planned manner. As such, Scrum adopts an empirical approach—accepting that the problem cannot be fully understood or defined, focusing instead on maximizing the team’s ability to deliver quickly and respond to emerging requirements.
There are several implementations of systems for managing the Scrum process, which range from yellow sticky notes and whiteboards, to software packages. One of Scrum’s biggest advantages is that it is very easy to learn and requires little effort to start using.

Roles
A number of roles are defined in Scrum. All roles fall into two distinct groups—pigs and chickens—based on the nature of their involvement in the development process.

“Pig” roles
The Pigs are the ones committed to the project in the Scrum process—they are the ones with “their bacon on the line” and performing the actual work of the project.
ScrumMaster (or Facilitator)
Scrum is facilitated by a ScrumMaster, also written as Scrum Master, whose primary job is to remove impediments to the ability of the team to deliver the sprint goal/deliverables. The ScrumMaster is not the leader of the team (as the team is self-organizing) but acts as a buffer between the team and any distracting influences. The ScrumMaster ensures that the Scrum process is used as intended. The ScrumMaster is the enforcer of rules. A key part of the ScrumMaster’s role is to protect the team and keep them focused on the tasks in hand.
Team
The team has the responsibility to deliver the product. A team is typically made up of 5–9 people with cross-functional skills who do the actual work (design, develop, test, technical communication, etc.).
Product Owner
The Product Owner represents the voice of the customer. He/she ensures that the Scrum Team works with the “right things” from a business perspective. The Product Owner writes customer-centric items (typically user stories), prioritizes them and then places them in the product backlog. A Product Owner can be a member of the Scrum Team but cannot be a ScrumMaster.
According to original Scrum, Product Owner is in a "pig" role. However, if the Product Owner does not have involvement regularly, he/she may be considered as a "chicken" .

“Chicken” roles
Chicken roles are not part of the actual Scrum process, but must be taken into account. They are people for whom the software is being built.
Stakeholders (customers, vendors)
These are the people who enable the project and for whom the project will produce the agreed-upon benefit[s], which justify its production. They are only directly involved in the process during the sprint reviews.
Managers
People who will set up the environment for the product development organizations.