IMDSv1 and IMDSv2 refer to two versions of the Instance Metadata Service used by cloud providers like AWS to deliver information about virtual machines to applications running on them. IMDSv1 allows direct HTTP requests to access metadata, which can be vulnerable to certain attacks, such as server-side request forgery (SSRF). IMDSv2 improves security by requiring a session-based token for access, making it much harder for unauthorized users or malicious code to retrieve sensitive metadata. The adoption of IMDSv2 is recommended to enhance the security of cloud environments.