What means flash program ecu in a car?

The ecu (or PCM) is the drivetrain computer. A flash update is just like a Windows or Mac program update. The manufacturer has altered the code and it has to be installed on the computer. The shop uses a bi-directional scan tool to load in the new software.

They do the same thing when they install a rebuilt computer--they have to install the software.

Car ECU progammer is used for reading and programming ECU content of eeprom file (or ROM memory with maps if eeprom physically not present). there have many different ecu modify * re-programming tools from vipprogrammer.com