What is the main characteristic of parenteral administration?

The main characteristic of parenteral administration is that it involves delivering medication through injections. This method bypasses the gastrointestinal tract, which is a significant distinction from other routes such as oral or nasal administration. Parenteral administration allows for the rapid onset of action and can be used to deliver medications that cannot be effectively absorbed when taken by mouth, such as certain proteins or steroids. It includes various routes like intravenous, intramuscular, and subcutaneous injections, making it a versatile option for medication delivery in both hospital settings and outpatient care. The other choices refer to routes of administration that either involve the gastrointestinal system or external application, which do not align with the definition of parenteral administration.