Nursing home
A 
nursing home is a facility providing permanent nursing care, 24 hours a day, as well as social and medical services; supporting residents with their elementary activities of daily living. Residents include elderly or seriously ill people, and such with physical and mental disabilities.
How to tag?
Nursing homes often consist of a building that stands on a campus with some green areas for short walks. Preferably the campus should be tagged.
Structured tagging
The modern tagging approach uses the high-level tag amenity=social_facility and specifies the facility as social_facility=nursing_home. The target group can be marked with social_facility:for=*, e.g. senior, disabled, mental_health.
This tagging approach allows to differentiate between similar facilities, see for example social_facility=assisted_living, a residential facility providing some support, such as access to a nurse and an emergency call system, but the residents are more independent (e.g., have own flats).
Please note that in the initial phase of the tagging approach (Oct 2010 - Jun 2016), Nursing Homes were subsumed under the value social_facility=group_home, with further tagging the target group. If you know a Nursing Home still tagged Group Home, better fitting the definition above, please migrate the tag to social_facility=nursing_home. Please check each case individually, Automated edits are discouraged.
Older tagging
Before the introduction of the amenity=social_facility tagging, amenity=nursing_home had been used and can still be found in the database.