TSP = Tri-Sodium Phosphate. A very strong, highly alkaline detergent cleaner available at paint and hardware stores - while big boxes may carry it, don't be fooled by the TSP substitutes or "phosphate free" TSP (wouldn't that just make it "TS"?). It's great for general cleaning, removes grease and heavy dirt, but always follow package directions when using (too strong a mixture can remove existing paint, damage metal and burn skin & eyes) - (this is NOT one of those products that "if 1/2 cup per gallon of water cleans this good, then 2 cups per gallon of date must be amazing.." - yeah, don't do that)...ALWAYS rinse surface with clean water following a TSP wash.
For lighter cleaning and surface prep, consider using a product like Soilax or Dirtex Powder (not aerosol), both are good utility cleaners, phosphate free and non-sudsing (so clean water rinse isn't necessary). Good luck.