A passive candidate is someone who is not looking for a job but would consider the right one. They are not browsing job boards or sending applications, yet a well-judged approach about a genuinely good fit can still tempt them. Because they are already employed and usually doing well, passive candidates are often the strongest people in a given market, which is exactly why they are worth the extra effort to reach.
They also will not come to you. A passive candidate never sees your job ad, so the only way to reach them is to go out and find them and start a conversation, which is what sourcing is for. And since they are in no hurry, the conversation often plays out over weeks or months rather than in a single application.
That is where a talent CRM and a credible employer brand earn their keep. Keeping in touch with promising passive candidates until the timing is right, and being a company they already think well of, turns the occasional lucky approach into a reliable source of strong hires. Reaching passive candidates is slower than collecting applications, but for senior and specialist roles it is frequently the only thing that works.