Lol, interrogatories is not a word that comes up in casual conversation much.
For anyone wondering: interrogatories are a set of written questions you send to the party. And Federal Rules of Civil Procedure , along with local rules, have specific requirements about the format - how much space, how it has to be numbered, etc.
Deposition - think formal interview with lawyers and a court reporter (no judge).
Generally, absent a court order, interrogatories and depositions are only allowed for parties to the case and any expert witnesses.