OS X is Darwin underneath, which is to say that it employs the standard BSD UNIX networking stack. NetInfo is an application program which comes from NextStep/OpenStep and is defined by Apple thusly:

NetInfo is a directory system that is built into computers running Mac OS X and Mac OS X Server. It facilitates management of administrative information used by Mac OS X computers. For example, NetInfo lets you centralize information about users, printers, servers, and other network devices so that all Mac OS X computers on your network, or only some of them, can have access to it. It helps you set up and manage home directories for Mac OS X users on multiple, integrated Mac OS X Server systems. And it simplifies day-to-day management of administrative information by letting you upgrade information that's used across the network in one central place. For more information on NetInfo, see the document titled "Understanding and Using NetInfo," available at www.apple.com/macosx/server.