"Vendor vaporware" refers to software or services that disappear because the company providing them ceases operations. This can happen due to financial issues, acquisitions, or other unforeseen circumstances. It's a significant concern because organizations invest substantial resources (time, money, and data) into these systems. If the vendor vanishes, users can lose access to their tools, systems, and critical data, potentially crippling their operations and mission. The source highlights how this happened during the dot-com collapse and continues to be a risk.