There are three types of contamination - biological, chemical and physical.
Chemical means bleach or solvents spilled into the food making them unsafe.
Physical means stuff that falls into the food that is not supposed to be there - debris, rat droppings, bugs, hair etc.
Biological means disease containing bacteria means molds, yeasts toxins, viruses etc. i.e. weather a food is prepared properly and if it is shelf stable or required refrigeration to...