1. A system for classifying things into groups
   "The librarian's pigeonholing system made it easy to find books on specific topics";
   - grouping

1. Place into a small compartment
   "The secretary pigeonholed the incoming mail for each department"
    
2. Treat or classify according to a mental stereotype
   "I was pigeonholed as a lazy Southern European";
   - stereotype, stamp

Type of: assort, class, classification system, classify, lay, place, pose, position, put, separate, set, sort, sort out

Encyclopedia: Pigeonholing