"Migration" is the process of migrating off-topic questions from a Stack Exchange site to another.
Migration is the operation that occurs when a question is deemed more appropriate for one of the other sites in the Stack Exchange network. Migration occurs when a question is closed, and three of the five users (four on Stack Overflow) voted to close the question as "off-topic because…" and then selected "This question belongs on another site in the Stack Exchange network." The question (and all of its answers) are copied to the new site, and the original question is closed.
Questions should only be migrated when:
- The question is off-topic for the current site
- The question is on-topic for the target site
- The question is of good quality
For more information, see What is migration and how does it work?