The terms 'opportunism' and 'opportunist' have been used for many years in various fields encompassing politics, social science, economics, and life sciences. However these terms are still ill-defined. The inter-relationship between the various meanings in different given contexts is discussed under the special aspect of micro-organisms, and in particular Candida albicans, which together with Pseudomonas aeruginosa, is most often addressed as an opportunist or suspected of opportunism.