Is put inside of the house in which it is going to be installed for several days so it can "adapt" to the temperature and humidity conditions in the house prior to installation.
IF the flooring was kept in a controlled enviroment prior to being brought into your house, it should minimize any problems you might have.
But, if the flooring came from a high humidity location, and your house is dry, you will have small gaps open between the individual boards as they dry out. IF it came from a very dry location, and your house is humid, there is a chance they could swell enough to cause the floor to buckle.
The tendency to do the above depends on the width of the floor and the extremes in temperature (and more importantly) humidity. A floor that is only 8 to 10 feet wide (perpendicular to the direction of the boards) would not have much tendency to do either of the above. Also, oak does not have as much tendency to expand and contract as say ash.
Bottom line, I would make sure your installer is aware of your concerns, and is willing to redo your floor if a problem develops. I don't think you will have a problem, but better safe than sorry.