Offer acceptance rate is a simple ratio, the number of offers accepted divided by the number of offers made, and it is one of the most revealing numbers in hiring. A high rate means the people you choose want to join you. A low rate means something is going wrong late in the process, after you have already spent most of the effort, which makes each declined offer especially costly.
The causes are usually a small set: an offer that is not competitive on pay, a process that moved too slowly and let a faster company get there first, or an experience along the way that left the candidate cool on the company. The value of the metric is that it points you at the late-stage problems that other numbers miss.
A slow process is the most common and most fixable culprit. Strong candidates are usually in more than one hiring process at once, and the offer that arrives first, from the company that felt like it wanted them, often wins even against a slightly better one that comes late. Closing the gaps that delay an offer directly lifts the rate.