In HTTP Referrer, the Component Type protocol refers to the part of the URL that specifies the protocol used to access the referring page. The protocol component is typically either "http" or "https" and indicates whether the referring page was accessed over a secure (https) or non-secure (http) connection. This information can be useful in determining the source and context of the referral traffic to a website. For example, if a website owner notices a significant increase in referral traffic from an https protocol, it may indicate that a new partner website has started linking to their site using a secure connection.
