Yes, there really is such a thing! Used to be you could find this essential sewing notion just about anywhere, but now it's getting harder and harder to come by.
What's it for? Why BASTING quilts, of course! Thread-basting is what we USED to do before those annoying little brass safety pins were invented, or the basting gun, or basting spray or fusible batts.
What's the advantage? Well, it's a kinder, gentler way to baste. Layer your quilt and thread up a nice long needle. Plunk a big knot at the end of your thread and park it on the TOP of the quilt for easy removal later. Start making huge stitches through the fabric sandwich. I prefer to baste in a grid, stitching horizontally, then vertically, as I move from one end of the quilt to the other.
Your fingers won't hurt like they do after pin-basting, your sandwich won't wiggle because thread basting keeps all the layers flat and together. There's no chance of poking a hole in your handiwork either, and you won't have to continually smooth and adjust the layers to keep the wrinkles away. (You won't accidentally find yourself stuck to the floor after your basting session either.)
So why not just use "regular" thread? Because the beauty of basting thread is that it can be pulled out without harming your quilting stitches. It breaks very easily. (It's supposed to!) Best used with big-eyed, long needles, not "betweens."
1000 yards of 100% cotton basting thread. Blister-packed.