When you're using an Ancestry database like Connecticut, Church Record Abstracts, 1630-1920 which was created from a book or series of printed books, browse back to the beginning of the book to look at the title page and front matter. Usually the abbreviations for the book will be listed on a page before the main body of the book.
Screenshot from Volume 1, Ashford
The abbreviations for this series of books are also in the About the Database information which can be found on the main search page for the database. You do not need to have an Ancestry subscription to read the About the Database information.
Whenever you are using images from a printed book, use the entire book (including the front matter and indices) to make sure you're getting the most information you can out of the entry you searched for.
We also need to look at Ancestry's Source Information:
Can we find clues on the website of the original repository?
The Connecticut State Library has a presentation slide deck on Slideshare, Genealogical Indexes at CSL. Slides 29-33 cover the Church Record Indexes.
Since these are indexes, the abstracts aren't intended to be used on their own. You need to use the references to find the original records. The slide deck says
Many of the church records have been microfilmed by the LDS, and are represented in the Family History Library catalog: www.familysearch.org.
The front matter of the book (image 3 in Ancestry's viewer) says:
This volume [covers] Farmington, First Church of Christ, (Congregational) from 1652-1938. This list was taken from volumes 1, 2, 3, 4, 5, 6, & 7 of the nine original volumes ...
This list was also taken from a set of cards based on a copy of some of the Church Records ... printed in ... The New England Historical & Genealogical Register
The church records on FamilySearch: Church records, 1652-1938 are on two FHL films which are restricted, so you'll have to wait until you have access to a FHC. However, your LUSK, LUSKE entries are apparently in Volumes 39 and 40 of the Register. You can look for those volumes (on Google Books, or on the Internet Archive) or look at them on Ancestry: The New England Historical & Genealogical Register, 1847-2011. Look at the Browse box on the side of the search page to find Volume 039 (1885) and Volume 040 (1886).
If I'm reading the index page correctly, the entries are on:
NER 40 page 360, NER 39 page 341, NER 40 page 31, NER 40 page 156, NER 39 page 242, NER 39 page 339
Let's put these in order.
I'll replace the links to Volume 39 when I find a copy that isn't from Ancestry.
Some volumes of The Register are also available at AmericanAncestors.org, the website of NEHGS.