What is excretion? Why is it important to living things?

Excretion is the elimination of products from the body.

The body needs to excrete waste products in order to maintain its homeostasis. For example consider what would happen if there was no excretion? the waste products would pile up in the body and cause major problems. Thus in order to maintain the normal working condition of the body, the body eliminates waste products ( urine, bowel, CO2 and many others).