A Fixed license is permanently attached to a user.
A Node Locked license is fixed to a node/host.
A Floating[b/] is not attached to any one user. There are a certain number of licenses available from the license server and are served out as requested. If all are served (in use) then none are availabe to the next requesting user and that user will have to wait until one is available. Remember, amateurs built the Ark, professionals built the Titanic.