What does the patent application publication date mean?

eighteen months from the date of application shall be the date of publication. According to the inquiry of knowledgeable people, the publication date of patent application refers to the date when the patent department, after receiving an application for a patent for invention, considers that it meets the requirements of the patent law after preliminary examination, and it will be published 18 months from the date of application. This date is also called the publication date, and it can also be published as soon as possible at the request of the applicant.