Post-hoc questions are "after the fact questions," meaning that after the first round of analysis in a study, the researchers decide to deviate from the original plan of analysis by adding more questions to the survey/questionnaire to collect more data.
Allen, M. (Ed.) (2017). The sage encyclopedia of communication research methods (Vols. 1-4). Thousand Oaks, CA: SAGE Publications, Inc. https://doi.org/10.4135/9781483381411