Respondent is the term for the party advocating against overturning a previous ruling during an appeal. Defendant is correct in this case because this is not an appeal.

The terminology varies quite widely from place to place, but it's common for the word "defendant" to be used in both criminal and civil cases in the USA. Respondent's correct too.

A lot of times you'll even see official documents not really pick a side on the question of terminology. They'll say things like "defendant/respondent" or "petitioner/plaintiff".

The context here is all cases.