A SecureCRT 9.0 license key is a unique alphanumeric code provided by the software vendor, VanDyke Software, to activate and register a copy of SecureCRT 9.0. The license key serves as proof of purchase and allows users to access the full range of features and functionalities offered by the software. The license key is typically generated based on the user's product serial number, which is used to identify the specific product and version.