[hnbroseph]

i don't think the act of defining a term for later usage in an argument can be described as "no true scotsman", which is typically a mid-argument dismissal of a counterexample that contests a generalization.

to be such they would have had to (for example) been in the midst of debating the topic, and said something like "but a real abortion..." where their operating definition of "abortion" was effectively changed.

[astine]

The term for this is a "stipulative definition." [1] It's only a fallacy if one does not clarify that one is using a stipulative definition instead of a more common one.

1. https://www.thoughtco.com/stipulative-definition-1692143

[dragonwriter]

Even if one is clear about the definition in use, it's the fallacy of equivocation if it is used to counter an argument using a different definition.