Seat License: Its specific to a machine. If you have 5 Pc's with QTP installed on it , 5 separate seat licenses are required(one license per machine)
Concurrent License: Concurrent licenses are configured on a license server provided by HP/Mercury. You must be on a network and should have a license server name or IP address of the server where the concurrent licenses are hosted. Multiple users can use the QTP at a same time on multiple PC's but again it depends on the number of concurrent licenses installed. Lets take an example:- Let say there are 50 Pc's with QTP installed on it , 20 Testers and 10 Concurrent Licenses. Only 10 testers out of 20 can run the QTP at the same time as there are only 10 Concurrent Licenses.