A pipeline is typically shown as columns or stages, such as new, screened, interviewing, offered and hired, with a count of candidates in each. Recruiters use it to see where people are waiting and where the next hires will come from. A pipeline with plenty of applicants but nobody at interview stage, for example, suggests screening is the bottleneck.
Pipeline health is about flow as much as volume. Candidates who sit at one stage for too long often withdraw, so teams track time in stage as well as counts. Keeping stages up to date in the ATS, moving or closing candidates promptly and keeping strong runners-up warm for future openings all help roles fill without starting from scratch.