Yes, it means the shutter is open for a long time. How long, of course, depends on the target.
With a DSLR, you can make many shorter exposures (each still considered to be a "time" exposure) and add them together to make a single image with the equivalent of a much longer exposure.
For example, I once photographed a comet during extremely windy conditions. I used a very heavy mount (an AP900) with a very small telescope (a Tak Epsilon 130) and a DSLR to make twenty 30-second exposures, then stacked them together. This allowed me to avoid wind-shake in the images and still get an acceptably bright final image. I made the image so it would give the same look and feel as a visual observation. Given the winds (gusts to 30 mph!), I was lucky to get any image at all. If I had tried to make several 10-minute images, not a single one would have been left undisturbed by the wind.
You can use this technique to good advantage on dimmer targets like nebulae and galaxies.
A good introductory text is Robert Reeves' Introduction to Digital Astrophotography: Imaging the Universe with a Digital Camera.