FlexNet Publisher Licensing, also known as FLEX and previously FLEXlm licensing, is a certificate-based, run-time licensing service sold by Flexera Software and is used throughout the industry. The certificate is an encrypted "key," which resides in a "license file". Applications automatically try to check-out a license by providing the "key" to the FLEX services. These services reside on a local machine or a network server.
NOTE: License check-in and check-out happen automatically when an application is open and closed; check-in and check-out do not require a specific action on the part of the user.