Wiktionary defines them as:

• Those who perform a particular kind of skilled work.
• Those engaged in an industry or group of related industries.
• The skilled practice of a practical occupation.

dtd.wisconsin.gov defines them as:

• industrial/manufacturing trades
  • Electrical and Instrumentation Technician
  • Industrial Maintenance Electrician
  • Industrial Pipefitter
  • Injection Molding Machine Setter
  • Machinist
  • Maintenance Mechanic
  • Metal Fabricator
  • Mold Maker
  • Pattern Maker
  • Tool and Die Maker
• construction trades
  • Bricklayer
  • Carpenter
  • Cement Mason/ Concrete Finisher
  • Construction Craft Laborer
  • Electrician (Construction)
  • Electrician (Residential)
  • Environmental Service Technician/ HVAC Installer-Technician
  • Glazier
  • Heat and Frost Insulator
  • Ironworker
  • Laborer (Construction Craft Laborer)
  • Operating Engineer/ Heavy Equipment Operator
  • Painter and Decorator
  • Plasterer
  • Plumber
  • Roofer & Waterproofer
  • Sheet Metal Worker
  • Sprinklerfitter
  • Steamfitter (Construction)
  • Steamfitter (Refrigeration/Service)
  • Taper & Finisher
  • Teledata Communications
  • Terrazzo Worker
  • Tile Setter
• service trades
  • Barber/Cosmetologist
  • Child Care Development Specialist
  • Cook/Chef
  • Correctional Officer
  • Electric Line Worker
  • Fire Service
  • Funeral Director
  • Metering Technician