The act of a single individual infiltrating a conversation that is among a group unknown to him or her.
Derived from the words "pedestrian" and "espionage".
A group of friends are walking to a party, when all of a sudden they notice some random person walking among them and eavsdropping on their conversation. They don't know this person, but he is attempting to go along undetected.
The individual that attempted to integrate himself into the group has committed Pedestrionage.