Halliday & Matthiessen (1999: 610-1):
The human individual is at once a biological “individual”, a social “individual”, and a socio–semiotic “individual”:
as a biological “individual”, s/he is an organism, born into a biological population as a member of the human species.
as a social “individual”, s/he is a person, born into a social group as a member of society. “Person” is a complex construct; it can be characterised as a constellation of social rôles or personæ entering into social networks …
as a socio–semiotic “individual”, s/he is a meaner, born into a meaning group as a member of a speech community. Meaner is also a complex construct. …
These different levels of individuality map onto one other: a meaner is a person, and a person is a biological organism. But the mappings are complex; and at each level an individual lives in different environments — in different networks of relations.