Referral traffic, in the context of Google Analytics, refers to the portion of website traffic that originates from other websites or domains. This type of traffic occurs when users click on links placed on external sources that direct them to your website. By tracking referral traffic, Google Analytics provides valuable insights into the effectiveness of your external link-building strategies and partnerships. Monitoring referral traffic enables website owners to understand which external sources are driving engagement and conversions, allowing them to optimize their marketing efforts accordingly.