I can give you a simple answer but it is way more complicated: Vaccines are trace amounts of material that are introduced to our immune system so that when a pathogen enters our body our immune system will recognize it and destroy it. Vaccines have been utilized in healthcare for a very long time. It is a good sign that you want to know more.
For all of medical history (and in laymen's terms) a vaccine was a manageable amount of a disease that would allow the body to build up a defense against that disease so if the body came in contact with that disease our bodies had the blueprint to fight it off.
Why did the CDC change the definition of vaccine?
Why do it under without scientific review or debate?
Why not call it something else? The word vaccine already existed and had a definition
Why was it done under darkness after selling the world on a 'vaccine' when in fact it wasn't a 'vaccine' it was a 'substance used to stimulate' instead of the definition that lasted since vaccines were found to help fight off diseases
This doesn't give you any pause? It doesn't seem odd to change the definition to fit what was sold to humanity? Odd how the scope of the definition is now significantly broader isn't it.
Why are the manufacturers, suppliers, distributors, providers not legally responsible for the covid vaccine if you feel it made you sick or if you have side effects? That seems odd for something that was mandatory to a huge chunk of the human race.