What does washed sperm mean?

What does 'washed sperm' mean?

Washing or spinning the sperm is a laboratory technique for separating sperm from semen and separating non-motile sperm from motile sperm.

The ejaculate is mixed with a washing medium followed by centrifugation (spun at high speed). The sperm rich fraction left at the end of this spinning process is mixed with more washing medium and the process repeated 2-3 times until only the highest quality sperm remain. This is then placed into a test tube ready for insemination.