http://www.daytonnursery.com/Christmas/Grave%20Blankets.htm#Standard%20Blanket
there is a link to show you what the grave blankets are. Hope this helps. Not sure if I am supposed to post links to sites or not but i didnt know how else to explain it.

There are different terms: grave covers, grave blankets or grave pillows.

In winter, most cemeteries have rules about no fresh flowers, etc. At Christmas, many people put the above-mentioned at gravesites. Usually, they're evergreens with whatever trimmings.

My Mom's 100th birthday (her first after passing) was in November, and so I ordered one without Christmas trimmings that would be suitable for then. Yesterday, I went and added Christmas trimmings to it for December.

If the grave you're honoring is in an outdoor cemetery, you will see many wreaths, blankets, etc., now but even closer to Christmas.
Hope this helped along with links provided by another poster.

I am not real sure what a grave cover is,I am going to try to find out.A friend of my daughter told us that she makes the covers for her loved ones.She said that she got chicken wire from the farm store.Cut the wire to the size that she wanted.Put silk flowers and other decorations in the holes of the wire.She says that she changes the flowers with the changeing of the seasons.I think that it would be special to make these.