Any relative, friend or partner who has a significant personal relationship and provides assistance (physical, social, and/or psychological) to a person with a life-threatening illness.
These individuals may be primary or secondary caregivers and may or may not reside with the person receiving care.
Caregiver is the word used in US, Canada. Carer is the word used in UK, NZ, Australia.
The words may be prefixed with "family" "spousal", "child" to distinguish between different care situations.
Hudson, P. and Payne, S. Family careers in palliative care: a guide for health and social care professionals. Oxford. Oxford University Press. 2009. p 284.
Caregiver: anyone who provides care.
Formal caregivers are members of an organization and accountable to defined norms of conduct and practice. They may be professionals, support workers, or volunteers. They are sometimes called “providers.”
Informal caregivers are not members of an organization. They have no formal training, and are not accountable to standards of conduct or practice. They may be family members or friends.