Facebook reach rate refers to the percentage of unique users who have seen your content on Facebook. It measures the effectiveness of your posts in reaching a wider audience and increasing brand awareness. This metric takes into account both organic and paid reach, providing valuable insights into the impact of your social media strategy. A high reach rate indicates that your content is resonating with your target audience and has the potential to go viral, while a low reach rate may suggest the need for adjustments to your content or targeting.