Glossary
Respondent
The party who has to respond to a petition: typically the other side in a divorce, custody, probate, or appeals case. Equivalent in role to a defendant, but the term used depends on the type of case.
When a case is started by a "petition" rather than a "complaint," the other side is called the respondent instead of the defendant. This is just a matter of vocabulary: the legal role is the same.
Common contexts where you'll see "respondent": divorce, child custody and support, name changes, guardianship, probate, restraining orders, and appeals.