It's just a poorly written description of the argument. If I understand the argument correctly there's a difference between a blastocyst (collection of cells not yet developed) and a fetus.

Life began billions of years ago.

This phrasing is meant to hide a religious argument as a scientific one. The question they're really asking is "When does God insert a soul into a body?"

Even if it did start at conception, the real argument is about bodily autonomy. No one can be forced to donate any part of their body to keep someone else alive. Nobody can take your blood without your permission, why should women have their bodies taken without theirs?

I agree with the biological definition, "organism that can survive as an individual". Even if the fetus has a parasitic relation, it is capable of developing all functions to fit the full definition.
There are other definitions of 'life' and anyone is free to believe either way, but the more subjective question is: When does the fetus become a person?

This is fun. With that logic you'll be naming a tumour or parasitic infection.