What is the difference between ingestion, digestion, absorption, and elimination?
Ingestion is taking food into the mouth for example.
Digestion is when the ingested food is now broken down into smaller building blocks. This may be achieved by mechanical means (chewing, churning) and chemical means (digestive enzymes of stomach and intestines).
Absorption is when the digested building blocks are now absorbed into the bloodstream or lymphatic system through the intestines and then transported to various cells, tissues, organs in the body.
Elimination is when waste products produced during digestion and absorption or left over after use by cells, or undigested remaints is now expelled from the body either via the urinary system as urine, digestive system as faeces, respiratory system as gases or integumentary system as perspiration.
I am going to add one more concept, secretion, where glands secrete certain useful chemicals like enzymes or hormones that may aid in many life processes, including digestion.