How Far Is A Light-Year?

Stars other than our sun are so far distant that astronomers refer to their distances not in terms of kilometers or miles - but in light-years. Light travels at an incredible 300,000 kilometers (186,000 miles) per second. If you could travel at the speed of light, you would be able to circle the Earth's equator about 7.5 times in just one second.
Few of us can comprehend such a humongous number. Is there any way for us mere mortals to really understand how far a light-year is?