(from the Biblio Book Collecting Glossary: https://www.biblio.com/book_collecting_terminology/)
New
A new book is a book previously not circulated to a buyer. Although a new book is typically free of any faults or defects, "new" is not actually a description of condition as a new book may possibly display shelf wear from the shop or distributor supplying it or printing errors or defects from publishing that were not detected. The actual specifics of a new book may be hard for a bookseller to state or predict as they may be shipping one of any number of copies of the title to fill the order. This, as opposed to As New which describes a used book that is determined to be free of any faults or wear.
Used
‘As New’ - The book is pristine and free of any defects, in the same condition as when it was first newly published. The textblock is tight, showing no signs of prior use. The dust jacket, if there is one, is similarly free of any wear, flaws or defects.
‘Fine’ - A book in fine condition exhibits no flaws. A fine condition book closely approaches As New condition, but may lack the crispness of an uncirculated, unopened volume. Any flaws of any kind must be clearly noted as exceptions to fine condition, as in "small crease on FFEP, else fine". Fine condition is abbreviated as "F", or "F/F" when describing a book and dust jacket that are both in fine condition.
‘Very Good’ - Very Good condition can describe a used book that does show some small signs of wear - but no tears - on either binding or paper. Should not have markings or highlighting, except names inside the front cover. Any defects must be noted. (definition based on AB Bookman's Weekly)
A book in very good condition is often cited as the minimum condition requirement for most collectors. Books in grades less than very good, such as good, poor and fair (and the indeterminate acceptable) are not generally accepted as collectible copies, except in the cases of very rare books or manuscripts.
Very good is most commonly abbreviated as VG, but may also appear unconventionally as V. Good.
‘Good’ - Good describes the average used and worn book that has all pages or leaves present. Any defects must be noted. (as defined by AB Bookman's Weekly).
The oft-repeated aphorism in the book collecting world is "good isn't good." However, this can be a little misleading: while generally not considered an acceptable condition for collectors (except in cases of very scare material), a good condition book usually suffices as a reading copy.
Good is most often abbreviated in listings as G or Gd.
‘Acceptable’ - A non-traditional book condition description that generally refers to a book in Good or Very Good condition, although no standard exists for this term, and the word can be used to describe a wide variety of actual book conditions.
‘Poor’ - A book with significant wear and faults. A poor condition book is still a reading copy with the full text still readable. Any missing pages must be specifically noted.
‘Reading Copy’ - Indicates a book that is perfectly serviceable for reading. It may have a defect or damage.
As such, reading copy is not a collectible book, except perhaps on occasion as a placeholder in the completest's collection until a desirable copy can be acquired. A reading copy should not be confused with an advance review copy or advance reader's copy, both of which can have appeal to book collectors.
That said, although a reading copy might have defects, these defects should not be such that they inhibit the readability of the text. Examples of defects or damages that would not be acceptable in a reading copy would include torn or missing pages, excessive highlighting or underlining, text block separating from the spine or page stains that cover or obscure part or all of the text. Books with these flaws can at best be considered binder's copies when scarce or desirable, but often are best suited to be recycled.
Ex-Library -
A former library book, generally containing library acquisition and ownership stamped markings, and other typical indications of the library's use.
Books legitimately released from institutional libraries such as a school library, public library, historical society, university, etc. Also named "ex-lib" will be lower in resale value due to library card pockets, rubber stamp identification information on spine or title pages, catalog numbers inked or stamped on inside or outside of book, call tags, bookplates, and normal to excessive wear and tear to the book itself due to the library lending system. When a listing states ex-library be aware of the condition and reach out to the bookseller for photos or more information concerning the book.
What is a ‘First Edition’?
https://www.biblio.com/book-collecting/basics/what-is-a-first-edition/