Use this tag when referring to domains in relation to attributes, geodatabases and in the GIS field in general
Esri describes domains as the following:
Attribute domains are rules that describe the legal values of a field type, providing a method for enforcing data integrity. A domain is a declaration of acceptable attribute values. Attribute domains are used to constrain the values allowed in any particular attribute for a table or feature class. If the features in a feature class or nonspatial objects in a table have been grouped into subtypes, different attribute domains can be assigned to each of the subtypes. Whenever a domain is associated with an attribute field, only the values within that domain are valid for the field. In other words, the field will not accept a value that is not in that domain. Using domains helps ensure data integrity by limiting the choice of values for a particular field.
Attribute domains can be shared across feature classes, tables, and subtypes in a geodatabase.
For example, a feature class for water mains and a feature class that stores water laterals can use the same domain for the ground surface type field.