Animals show various degrees of adaptation aimed at taking advantage of available resources, but. . . most can be considered either specialists or generalists. Among plant-eating insects the more specific terms polyphagous, oligophagous, and monophagous are widely employed in relation to the variety of plant species they use. The majority of phytophagous insects are oligophagous. While they differ in their behavior from monophagous insects (which feed on only a single plant species), they are selective as far as which plant families or genera are acceptable. Other factors besides nutritional composition of the plant are important in guiding their behavior. Specialist animals exploit a particular resource: perhaps a particular plant part such as leaves or fruit, or perhaps a single plant species. . . By contrast, humans are extreme generalists. Like other omnivores such as rats, bears, pigs, and many primates, we eat a range of animal and plant foods. For omnivores, not only sensory perception but also the lessons learned from the physiological consequences of ingestion are important in determining food selection.
Source: wiktionary