So, have you ever told a lie to someone? Maybe you said you finished your homework, but really you were still working on it. That's called deception - when we don't tell the truth, either by lying or by hiding something.
Interpersonal deception theory is like a special way of studying how people lie to each other. It's like being a detective and trying to figure out who's telling the truth, and who's not.
Scientists who study interpersonal deception theory look at lots of things to figure out if someone is lying. For example, they look at how much someone blinks when they talk, or if they use lots of hand gestures. They also look at things like facial expressions and voice tone to try to figure out if someone is telling the truth or not.
Sometimes people try to hide the signs that they're lying, but scientists who study interpersonal deception theory are very good at spotting those signs. They know all the little clues that can give someone away when they're telling a fib.
So, in summary, interpersonal deception theory is a way of studying how people lie to each other. Scientists look at clues like body language, facial expressions, and voice tone to figure out if someone is telling the truth or not.