You walk along the street and you see someone you know to a certain extent. Enough to recognize their face and name and, perhaps, a couple of things about them. You say "how's it going?" but proceed along the street before listening to any reply, if any. Or, perhaps, being a bit more socially aware, you say "hello". They respond -- not expecting a reply either -- and you have created the first level of social interactions. You have acknowledged the existence of the other.
This is an important aspect of society. When there is no acknowledgement of another, it is the equivalent of the punishment of "shunning". Some see shunning as a "social death sentence". You don't exist, you are not part of the rest of the world. You might as well not be present. There is sometimes an imbalance where one person is considered "more important" than another -- for whatever reason, income, social class, caste, outward body shape/size/color/height. But, as long as acknowledgement happens, all are still connected as part of the society.
A danger sign exists when a person does not recognize another at all. It might be a "more important" person ignoring a "less important" person but lack of acknowledgement breaks societal links. That person should never be allocated more influence over others as they have indicated lack of social ability.
Breaking the social acknowledgement links can be done on purpose -- beyond the social penalty of "shunning". It is done during wartime. It is done during periods of xenophobia when the group becomes fearful of others. If a person is not acknowledged, they are no longer a person and anything can be done with, or to, them without remorse.
A middle level of social interaction works within the societal system that exists. As such, it will vary from culture to culture around the world. It centers on expectations and responsibilities. Often it is associated with social levels -- whether from lineage, income, or subgroup. Along with acknowledgement comes, often implicitly, expectations of how interactions will take place and how the process goes. Sometimes it is very formal and "codified" into the general society.
A higher level of social interaction involves full acknowledgement of the existence and worth of the other. A "namaste" between two. The acknowledgement is the base, the desire for understanding is much higher. In this case, "how are you?' expects, and receives, an answer and potentially a discussion.
Acknowledgement, interaction, understanding. A path forward.
