Definition
Multiposting means publishing a job posting on several job boards from a single tool, instead of entering it site by site. Incoming applications then flow back into the ATS, so you do not have to look for them in several inboxes.
Why it is useful
It saves time and lets you compare channels: which sites bring candidates who progress through the process, and which only bring volume. Two points of caution: wider distribution means more applications, so more answers to give; and some mandatory statements, such as Ontario's AI-use disclosure, must follow the posting to every site.
Concrete example
A small manufacturer posts a welder job on three job boards in a single operation. After a month, it sees that one board brought most of the candidates who reached the interview stage, and it decides to focus its budget there for similar roles. It still answers every applicant, whichever board they came from, because the candidate does not care which channel the employer prefers. Tracking the source of each hire, not only the number of applications, is what makes multiposting worth the effort.