A passive speaker (also referred to as a receptive bilingual or passive bilingual) is a category of speaker who has had enough exposure to a language in childhood to have a native-like comprehension of it, but has little or no active command of it.
Such speakers are especially common in language shift communities where speakers of a declining language do not acquire active competence. Around 10% of the Ainu people who speak the language are considered passive speakers. Passive speakers are often targeted in language revival efforts to increase the number of speakers of a language quickly, as they are likely to gain active and near-native speaking skills more quickly than those with no knowledge of the language. They are also found in areas where people grow up hearing another language outside their family with no formal education.
A passive language is a related term used in interpreting or translating. It is the language or languages from which the interpreter works. For example if an interpreter's job is to translate from German, Dutch and Swedish into French, then French is the active language while the others are passive.
AAIC Glossary: Passive language