As mentioned above, Search Services are made up of sets of Fields. These can be thought of as somewhat analogous to column definitions in database tables. A Field has a name and a type, and if being returned from a search it will also have a value, which is the result.
Fields may be marked as being 'Stored'. Fields marked in this way will cause the Index to physically contain relevant values extracted (see Extractor) from the database. This means that their values can be retrieved directly from the Index after a search and returned to the caller without the need to access the related record on the application database table. Note however that this does increase the Index size and may impact the performance of the search.
Fields may also be marked as 'Indexed' or not. Fields marked as such are searchable, and Fields not marked as such are not searchable. This feature is useful for fields such as unique IDs that may be desirable to store in the Index but not searched upon.
Note that Fields do not have to be marked as 'Stored' to be searchable.