Hi Ashone! Welcome to the Nexus 7 Forum!
As a quick answer to your question, rooting means giving 'super user' access to a device. So in other words many manufacturers 'lock' their devices software to prevent users from adding things like drivers or other capabilities and by 'rooting' a device it unlocks it so that the user can basically add anything to the device's software such as change it to a new operating system or alter the current one to add more functionality to it. I hope that helps.
If you have any other questions please start a thread in the appropriate discussion board such as 'help' or 'general discussion' since this is the 'New Member Introduction' thread. Thanks!