It looks to me like these three tags have a lot of overlap between them - so much that maybe we should to make them synonyms, remove one (or two?) of them or something.
The tag descriptions seem almost interchangeable to me:
Graphs are abstract representations of objects and their mutual relations, where the objects are 'nodes' and the connections among them are 'edges'.
Refers to network theory as part of the graph theory. For questions about neural networks, use our [neural-networks] tag.
Social network data consists of a collection of "nodes" (which can be any sort of entity - e.g. people, corporations) and "links" (which can be any sort of relationship - e.g. friend, sharing a board member).
Out of the 10 newest questions in
graph-theory, 5 include the
networks tag, and I'd argue that most others could include it too - for example, this one is about doing machine learning (specifically feature extraction) where the data has a graph structure (could just as well be called a network structuree or a social network).
I don't have a concrete suggestion yet - My first though would be to collapse all three into one tag, unless mathematical questions about Graph Theory (not in the practical sense of statistics or learning on networks data) are relevant here (which... I kinda think it isn't?).