Standard epidemic models use pairwise (graph) interactions. But real contagion — social influence, information spread, group infections — often involves higher-order interactions among 3+ agents simultaneously.
Hypergraphs generalize graphs: a hyperedge can connect any number of nodes. Group exposure creates discontinuous (bistable) transitions absent in pairwise models.
The threshold for epidemic spread changes non-trivially: even below the pairwise threshold, group effects can trigger explosive outbreaks.