Ribbons are slim strips of grass left behind when a sod field is harvested (in this photo, in a field of Floratam St. Augustine).
Ever notice how some turfgrasses will send out long stems with leaves attached? These runners will grow across the open spaces, develop roots, and fill in the harvested areas. In about 6-12 months, depending on the time of year, type of grass, and location, the field can be harvested again.
Thanks for asking!