publisher; publishing company
Refers to a business or company engaged in publishing books, magazines, or other printed materials.
He works for a major publisher.
The book was published by a local publisher.
出版社 is a more common and general term for a publishing company, while 出版業者 emphasizes the business or trade aspect.
Compound of 出版 (shuppan, 'publishing') + 業者 (gyōsha, 'trader, business operator').