This format is the format for SPSS statistics output files. A variation of it was .spo, now no longer used. See more info from IBM support ("Statistics output files (.spo or .spv) are generally not backward compatible; output files of the same type ( i.e., .spo or .spv) created in a later version of Statistics cannot generally be opened in earlier versions. Further, beginning with version 16, output files are written in the .spv format. It is not possible to read .spo format files directly into Statistics version 16 and later."). See also info on .spo from Wikidata and info on .spv from Wikidata, and Fileformat wiki on SPSS formats.