Answer:
Civil inattention.
Step-by-step explanation:
According to Erving Goffman, we often come across situations in public places where we are left with another stranger for a short period of time. These situations may occur inside elevators, public transport, office buildings, or anywhere in public spaces.
During these situations it has been observed that most people would greet each other with a slight head nod or a small gesture. However, they tend to ignore the presence of each other after that encounter. This phenomenon or behavior is referred as an example of civil inattention.
This is done to show the other person that we recognize the other person's presence though not necessarily looking for any interaction.