sphinx is configured to examine a data set via its indexer. the indexer process creates a full-text index (a special data structure that enables quick keyword searches) from the given data/text. full-text fields are the resulting content that is indexed by sphinx; they can be (quickly) searched for keywords. fields are named, and you can limit your searches to a single field (e.g. search through "title" only) or a subset of fields (e.g. to "title" and "abstract" only). sphinx's index format generally supports up to 256 fields. note that the original data is not stored in the sphinx index, but are discarded during the indexing process; sphinx assumes that you store those contents elsewhere.