Replacement refers to methods, which avoid or replace the use of animals in areas where animals would otherwise have been used.
Refinement refers to improvements to housing and care and procedures, which minimise actual or potential pain, suffering, distress or lasting harm and/or improve animal welfare in situations where the use of animals is unavoidable. Refinement also refers to the lifetime experience of the animal. There is evidence that refinement not only benefits animals, but also improves the quality of research findings.
Reduction refers to methods which minimise animal use and enable researchers to obtain comparable levels of information from fewer animals or to obtain more information from the same number of animals, thereby reducing future use of animals.