Splitting an automated test suite into multiple runs that execute in separate processes at the same time. This technique can be used to greatly reduce the time required for automated tests to run.
Test parallelization requires that tests are split in such a way that order dependent tests are unaffected. For example, if Test B requires that Test A must be executed first, Test A would generally be run first on the same process that executes Test B.
Many test frameworks provide command line flags or settings that make test parallelization easier. CI servers such as Jenkins often have the ability to execute tests in parallel.