op·ti·mum 
(ŏptə-məm)
(ŏptə-məm)n. pl. op·ti·ma (-mə) or op·ti·mums
1. The point at which the condition, degree, or amount of something is the most favorable.
2. Biology The most favorable condition for growth and reproduction.
adj.
Most favorable or advantageous; best.
[Latin, neuter sing. of optimus, best; see op- in the Appendix of Indo-European roots.]