Latin frog, bilingual is an adjective used to refer to any person who speaks two languages or what is written in two languages.
Examples: "the multinational company seeks a bilingual (Spanish-English) graduate candidate in management", «In the market of the work of our days, being bilingual is almost a necessity», «they presented a bilingual edition of the biography of the singer.
Bilingualism (the ability of a person to use both languages easily) can be native or acquired. If Mexican parents have a child who was born and raised in the United States, this child is a bilingual native because in him, he speaks Spanish while at school and in society it communicates in English.
By against, in the case of a person born and having lived all his life in France, but who did studies of German since the age of five years ending with dominate this second language perfectly in addition to their mother tongue (Spanish), it's acquired bilingualism.
The concept of bilingual is therefore associated with the mastery of two languages that can be used by an individual without distinction (that is to say, he is able to express themselves without problem in both languages). A subject who has knowledge of one language other than their mother tongue is not bilingual because he cannot speak fluently.
With globalization, bilingualism (or multilingualism) has become more common since trips and international communications have become massive.