The primary difference between indoor and outdoor lighting is the amount of moisture a light fixture can handle. You should never put an indoor light fixture outside. A build up of moisture inside the light fixture could result in a dangerous fire or spark. The good news is many of the same indoor designs are available outdoors too.
Wet vs Damp
Areas that have direct contact with water require wet rated lamps. These areas are typically subjected to rainfall, snow, or sprinklers. Usually walls and pathways. Areas that have indirect contact with water require damp rated lamps. These areas are typically porches and patio. Damp rated light fixtures are insulated enough to withstand moisture build up from the environment, but not enough to withstand direct rain or snow contact