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, bom into a social group as a member of society. "Person" is a complex construct; it can be characterised as a constellation of social roles or personae 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. For the socio-semiotic construction of the individual subject, see Thibault (1993) … .
These different levels of individuality map onto one another: 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.