Analyte: The substance (drug or molecule) being tested for (i.e. EtG, EtS, alcohol, benzoylecognine, etc)
Matrix (pl matrices): The tissue, body fluid, or substance being tested. Any tissue or substance can be tested but the most common matrices are urine, hair, blood, saliva, and fingernails.
Incidental Exposure: Environmental or other exposure to an analyte not typically thought of as a method of use of the drug (e.g. hemp oil contains marijuana, poppy seeds contain opium, mouthwash contains ethanol - none of the products are typically used to "get high" yet they contain the analyte and can "accidentally" cause a positive test).