The Commas Instead of Line Feeds field flag (flag number 131072) is used to replace Hard Returns (Carriage Returns or Paragraph Marks) with a comma and a space. On Reports, it also replaces character #255 on lists (like Serial Numbers and Alternate Codes) with a comma and a space allowing lists to print more than one list entry on each line.
See:
Report/Label Editor - Field Flags - All
Report/Label Editor Contents