Within the linguistic study of endangered languages, sociolinguists distinguish between different speaker types based on the type of competence they have acquired of the endangered language. Often when a community is gradually shifting away from an endangered language to a majority language, not all speakers acquire full linguistic competence; instead, speakers have varying degrees and types of competence depending on their exposure to the minority language in their upbringing. The relevance of speaker types in cases of language shift was first noted by Nancy Dorian, who coined the term semi-speaker to refer to those speakers of Sutherland Gaelic who were predominantly English-speaking and whose Gaelic competence was limited and showed considerable influence from English. Later studies added additional speaker types such as rememberers (who remember some words and phrases but have little or no grammatical competence and do not actively speak the language), and passive speakers (who have nearly full comprehension competence but do not actively speak the language). In the context of language revitalization, new speakers who have learned the endangered language as a second language are sometimes distinguished.

In contexts of language acquisition and language teaching studies, there is sometimes a distinction between native speakers and second language speakers, depending on whether the language was learned as a language of primary socialisation or after having fully acquired a first language. In contexts of multilingualism a bilingual speaker may also be described as a heritage speaker (although a heritage language actually refers to a language whose speakers have moved from the original area where the language was spoken: e.g. Welsh is a heritage language in Patagonia, but not in Wales) if they have not been as fully exposed to one of their languages, leading to a diminished degree of confidence in themselves as speakers, and sometimes also limited competence in one of their languages.

A rememberer knows individual words or phrases (sometimes entire texts) but cannot use the target language productively. Such persons are of particular interest when studying any endangered or dying language. Rememberers are contrasted with fluent or full speakers, who have a good command of the language, and semi-speakers, who have a partial command of it. The distinction between fluent speakers and rememberers is important in fieldwork, but accurately determining where a member of a language community falls on the speaker-rememberer continuum can be challenging.

A passive speaker (also referred to as a receptive bilingual or passive bilingual) 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 in which speakers of a declining language do not acquire active competence. For example, 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 fluent speaker is someone who has a good command of the language.

A semi-speaker is a speaker who has acquired at the least a basic linguistic competence in a given language but does not generally use it regularly in conversation. Their speech can contain erroneous forms. Semi-speakers are often among the most motivated and engaged participants in language revitalization projects. As languages become obsolete and speech communities shift to other languages, the earlier language is spoken less frequently and in fewer social domains. Many speakers learn the language partially, often with simplification and significant influence from the majority language. They are sometimes referred to as "semi-speakers", "quasi-speakers" or "rememberers".

The word "semi-speaker" was introduced by linguist Nancy Dorian in describing the last speakers of the East Sutherland dialect of Scottish Gaelic.