What is considered a caregiver?

It's different for everyone, but generally we are someone's caregiver if they need assistance with daily living and we provide at least some of that assistance. We are generally someone the care receiver trusts and can depend upon. There are people who are considered a "primary caregiver" (providing significant care) and also those who provide backup or occasional care.
Of course, there are professional caregivers such as CNAs in nursing homes.
Carol