Loading the operating system into the computer's memory is called booting. (No, it doesn't mean you have to "kick" the computer, even though sometimes you would probably like to.) The term "boot" comes from the concept of pulling yourself up by the bootstraps. As the computer turns on, some instructions in ROM tell the computer how to 'wake up', find the peripherals, and load the operating system into memory.
If the computer is turned on from the off position, it is called a hard boot. If the computer is reset while it is on it is called a soft boot. Most computers now have reset keys which allow you to soft boot the computer; with older computers the standard way to soft boot was to use the ctr-alt-del keys.
