In common parlance and in the narrower sense, Southern Min refers to the Quanzhang or Hokkien-Taiwanese variety of Southern Min originating from Southern Fujian in Mainland China. It is spoken mainly in Fujian, Taiwan, as well as certain parts of Southeast Asia. The Quanzhang variety is often called simply "Minnan Proper" (simplified Chinese: 闽南语; traditional Chinese: 閩南語). It is considered the de-facto mainstream form of Southern Min.
In the wider scope, Southern Min also includes other Min Chinese varieties that are linguistically related to Minnan proper (Quanzhang). Most variants of Southern Min have significant differences from the Quanzhang variety, some having limited mutual intelligibility with it, others almost none. Teochew, Longyan, and Zhenan may be said to have limited mutual intelligibility with Minnan Proper, sharing similar phonology and vocabulary to a small extent. On the other hand, variants such as Datian, Zhongshan, and Qiong-Lei have historical linguistic roots with Minnan Proper, but are significantly divergent from it in terms of phonology and vocabulary, and thus have almost no mutual intelligibility with the Quanzhang variety. Linguists tend to classify them as separate Min languages.
Southern Min speakers form the majority of Chinese in Singapore, with the largest group being Minnan Proper (Hokkien-Taiwanese) and the second largest being Teochew. Despite the similarities, the two groups are rarely seen as part of the same "Minnan" Chinese subgroups.