Attrition is the speed or rate at which something declines. In recruitment, you may hear the term 'employee attrition rates' from your clients now and again. What this means is that a company is losing staff due to natural reduction including resignation, retirement, or relocation.
Keep in mind; this term refers to natural reduction. Employee attrition rates would not include mass layoffs for instance. Discuss with the interviewer that you understand what attrition means, and what the primary causes of employee attrition are. The hiring authority is looking for your ability to recognize and understand your clients' pain points.