To groom is to "prepare or train (someone) for a particular purpose or activity."

It also has a more specific definition: "the act of deliberately establishing an emotional connection with a child to prepare the child for child abuse".

Today, I think people are using the word to mean a hybrid of the above two definitions, namely, to train or indoctrinate a child into sexual deviancy, even if the person doing the grooming does not take part in it directly.

I think some uses today are also just synonyms for indoctrination, which fits only within the more general definition of grooming.