A Kaspersky license key is a unique code that unlocks the full features of Kaspersky antivirus software. It's a 25-character code that consists of letters and numbers, which is used to activate the software and validate your subscription. The license key is usually provided when you purchase a Kaspersky product, either online or through a retail store. The key is linked to your specific product and allows you to access all its features, including updates, scans, and real-time protection.