GLP, or good laboratory practice, is a term introduced in the 1970s by the Federal Drug Administration (FDA) and the Organisation for Economic Co-operation and Development (OECD) to describe a system of regulation of laboratory testing.
The principles of GLP are designed to ensure that laboratory testing and results are of a good quality and are traceable. Testing that has been performed using the wrong materials, methods or equipment can be identified and discounted. Labs that use GLP are therefore more reputable than those who don't use GLP.
Following GLP means that analysts and management of laboratories must keep clear and accurate records of the testing procedure and the methods used. This has the effect of minimizing fraudulent claims by a laboratory because the paper trail can be referred to.
GLP necessitates having a written protocol to follow in testing and supporting documentation to ensure the procedures were followed correctly. This means that another analyst or laboratory can reproduce the testing exactly to ensure a result is valid.