A foreign language is a language indigenous to another country. It is also a language not spoken in the native country of the person referred to, i.e., an English speaker living in Guam can say that Chamorro is a foreign language to him or her. These two characterisations do not exhaust the possible definitions, however, and the label is occasionally applied in ways that are variously misleading or factually inaccurate.
Some children learn more than one language from birth or from a very young age: they are bilingual or multilingual. These children can be said to have two, three or more mother tongues: neither language is foreign to that child, even if one language is a foreign language for the vast majority of people in the child's birth country. For example, a child learning English from his English father and Irish at school in Ireland can speak both English and Irish, but neither is a foreign language to him. This is common in countries such as India, South Africa, or Canada due to these countries having multiple official languages.
In general, it is believed that children have advantage to learning a foreign language over adults. However, there are studies which have shown adult students are better at foreign language learning than child students. It is because adults have a superior ability of memorizing vocabulary which surely allows them to build vocabulary faster than children.[2] And their pre-existing knowledge of language, not to mention that children's knowledge of language is not as substantial as adults'.[3] As a fact, there is an example of a man named David Bailey who learned French only in 17 days and became fluent enough to have a conversation with native speakers.[4]