There isn't much information to what the word, "Principal" means, in the purple question mark.
Is there a definition library on FamilySearch for such terminology? I think it would be very helpful.
@ Christopher Stapleton thank you for your question in the Community of FamilySearch.
Looking up the definition of Principle; "Principal can refer to an individual party or parties, the owner of a private company, or the chief participant in a transaction."
In the case of indexing marriages the person referred to a Principal is the 1st person mentioned in the record, namely here John Birtwistle, to whom the other relationships refer such as Spouse, Principal's Father's names etc.
In the case of Spouse initially it refers back to the 1st person named and thereafter other Spouse's references refer back to her.
Here is an extract from a Knowledge Article in FamilySearch,
" The principal person in a historical record is the primary person involved in the event.
This chart shows common record types and the principal person for each one:
Birth certificatePerson who was bornMarriage certificateBoth the bride and the groom Census Head of household Death certificate Person who died
ObituaryPerson who died
I trust this has answered your question and thank you for participating in this invaluable work.
Kind Regards, Peter A Basford.
There is also a glossary for indexing terminology which includes the term Principal Person:
In the FamilySearch Research Wiki there is an article on Genealogical Terms that includes links to a Dictionary of Genealogy & Archaic Terms and also a link to an article with sources for acronyms and abbreviations.
I'm not particularly fond of that article as you can find better sites by searching for Abbreviations and Acronyms for Genealogy on the web. Rootsweb, Geni, and Ancestry all have really good easily searchable databases of genealogy terms that you will encounter in old records.
Speaking of the Glossary of Indexing Terms, there should be a link to it (among several other basic Indexing resources) under the “Quick Link” section of this forum. If we don’t share a common understanding of its terms, how can we effectively communicate about Indexing? And it should be kept up to date.