The imprint is the "brand name" under which a book is published. Most major publishers have at least a few imprints. Some of these imprints are organized into divisions, as subsidiaries, or "companies within a company," with their own editorial staffs, release lists, etc. Others are strictly brand names slapped on a book purchased and edited somewhere within the parent publishing company. Often publishers use imprints to organize and manage all their authors and books within a certain genre, e.g., fiction.
According to Wikipedia, Random House, the world's largest English-language trade book publisher, has more than 50 imprints.
Axis Publishing & Distribution Company, LLC currently has three imprints:
Axis Publishing - Non-fiction, self-help and do-it-yourself books;
XYLOPHONE Press -Children's picture and story books; and,
Xion Press - Fiction, graphic novels, poetry and other artistic expression books.