Put simply, this term means going out to a space, measuring it and noting the location of any elements (electrical outlets, light fixtures & switches, heating & air conditioning diffusers, etc.) that are important to the scope of your project or that might affect your design. FYI: When someone (a client, a building manager, a real estate broker, etc.) gives you a floor plan or a set of drawings, automatically assume that they’re inaccurate because 95% of the time they are. Therefore, if at all possible, it is necessary to (at the very least) take some quick measurements to make sure all is copasetic. You’ll be glad you did. We’ve learned the hard way.