Relationships between nodes in a network can be one-to-one, or they can be one-to-many.

The key attribute of one-to-many connections is that they are directed links, where the flow of the interaction is unidirectional. One-to-one relationships, on the other hand, are usually functionally reciprocal. Therefore, they're undirected. The interaction flows both ways.

In the example of Twitter discussed earlier, or other asymmetric-follow personal networks like Instagram or YouTube, there are central nodes with many followers (inbound directed connections), and there are marginal nodes without many followers. The marginal nodes in these examples are primarily observers, whereas the central nodes are content producers.

Central nodes with one-to-many relationships can broadcast to marginal nodes, whereas the interaction that flows back is usually small to non-existent (think of the relationship of a celebrity and their followers on Instagram or a TV network and their viewers).

Central nodes also can exist in one-to-one connection networks like Facebook (although they eventually ended up adding a one-to-many "follow" feature themselves), where some users have many friends and others very few. But the potential for disparity isn't as vast as it is with networks that allow for one-to-many networks.