What does public domain mean in regards to quilt patterns?

It means they have no copyright protection and the public can use them freely without any legal problem.

copyrights last something like 70 years after the person who owns the copyright passes away- then if a new application is not put in...it expires and goes into public domain where anyone can than use it for any purpose they want- they just can not copyright it again.

other things in public domain are lots of clip art-coloring book pages-
things that seem to be available everywhere-and usable in any way you want.

There is another time factor regarding copyrights.
The law that was in effect at the time of the copyright applies. At one time it was the life of the person plus 50 years.