A bilingual individual is traditionally defined as someone who understands and produces two or more languages on a regular basis. A bilingual individual's initial exposure to both languages may start in early childhood, e.g. before age 3, but exposure may also begin later in life. Equal proficiency in a bilingual individuals's languages is rarely attested as it typically varies by domain. For example, a bilingual individual may have greater proficiency for work-related terms in one language, and family-related terms in another language.