The best, the most favorable, the most suitable, or the most advantageous condition or result
The word optimum in biology is often used to denote to a condition or a result that is favourable or best for a particular living entity. For instance, the term optimum pH refers to the pH resulting in maximal activity of a particular enzyme. Differing pH levels affect the shape of an enzyme. Each enzyme has an optimal pH at which the enzyme works best. Enzymes in the intestine for instance work best at pH of 7.5 (therefore, the optimum pH). The enzymes in the stomach have a different optimum pH though. The enzymatic activity in the stomach is best at pH of about 2. In terms of microbial growth, the term optimum pH pertains to the pH that is most favourable to the growth and survival of a living organism. Bacteria for instance have different optimum pH for growth. In fact, bacteria that grow best at an optimum pH of 7.0 (i.e. neutral pH) are called neutrophiles. Those that grow best below the neurtral pH are referred to as acidophiles whereas those that grow best above the neutral pH are called alkaliphiles. Apart from pH, another factor that has optimum ranges for enzymes and living organisms is temperature. Similar to optimum pH, an optimal temperature would be one that is best or the most favorable to enzymatic activity and to the growth of living organisms.
Word origin: Latin optimus (best, very good)