The look command searches through the system dictionary or lines in some other sorted list for a word. I often use look to check my spelling of a word. Suppose I want to know if inoculate is spelled correctly. I would type look inoculate. If inoculate is in the system dictionary (which it is) it is echoed to the terminal, and I know that the spelling is correct. If it is not in the system dictionary, it is not echoed to the terminal.