This data format is used in \(\le\) StoX 2.7 to define strata polygons.
A data frame used in early versions of StoX to define strata polygons, which combine one variable with strata names and one variable consisting of multipolygon.wkt strings. Well-known text (WKT) is a text markup language for representing vector geometry objects.
Additonal information on WKT multipolygon specification and StoX can be found here:
https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry
Johnsen, E., Totland, A., Skålevik, Å., Holmin, A. J., Dingsør, G. E., Fuglebakk, E., & Handegard, N. O. (2019). StoX: An open source software for marine survey analyses. Methods in Ecology and Evolution, 10(9), 1523-1528. doi:10.1111/2041-210X.13250