Cumulative Layout Shift (CLS) is a core web vitals metric, measures singnificance of unexpected layout shifts on a page. CLS is a web peformance metric that helps you understand the delightfulness of the user experience. 

CLS is a relatvely new metric that measures or calculates the instability of content by summing shift scores across layout shifts that dont occur within 500ms of user input with the website. CLS is unique that accurately mesaures the user experience more than anything else.