Candidate experience is how it feels to go through your hiring process from the applicant's side. It covers everything they encounter: how clear the job description was, how easy the application was, how quickly you responded, how the interviews felt, and how the final decision was communicated. It is the sum of many small moments, and candidates remember it long after the process ends.
It matters for reasons that show up directly in your results. A good experience makes candidates more likely to accept an offer and more likely to recommend you to others, while a poor one costs you strong people and damages your reputation. Because candidates talk, the experience you give even the people you reject shapes how the next round of applicants sees you.
The encouraging part is that most of what makes candidate experience good is within your control and costs little: be clear about the role, respond promptly, keep people informed, run a fair and respectful interview, and close the loop kindly with those you turn down. Speed and communication do most of the work. A candidate rarely minds a no nearly as much as they mind silence.