The email share rate refers to the percentage of email recipients who choose to share the email with others, either by forwarding it or using the built-in share options. This metric is often used by businesses to measure the success of their email marketing campaigns, as a higher share rate indicates that the content resonated with the audience and encouraged them to spread the message to their own networks. A high email share rate can also lead to increased brand awareness and potential new customers, making it a valuable metric for businesses to track.