The study of language maintenance and shift (LMS) has attracted a large body of empirical work in language policy and planning (LPP) contexts, including allochthonous (immigrant) and autochthonous (indigenous) languages. However, some critical ontological questions that relate to the scope and terminology of language maintenance studies remain unanswered, and there seems to be a lack of consistency in the definitions of the relevant terms, such as what 'heritage' language refers to, whose heritage it is when a language can be classified as a heritage language, and what 'language' is at all. Therefore, this review summarises existing literature on LPP for language maintenance by employing a scoping review methodology, providing an overview of empirical studies of LPP in migration context over the past two decades (2001-2023), focusing on terminology, geographical settings, research focus and methods. The findings reveal that most studies (66.3%) use the term 'heritage language' to refer to the 'language of transnational minorities' among other terms. The results also highlight geographical gaps and imbalances in the literature, calling for more LPP studies from South American and East Asian contexts. In addition, further investigations are needed to explore the transnational and translocal aspects of language maintenance.