Motifs are recurring, statistically significant subgraph patterns in a network. Milo et al. (2002) showed different network types have characteristic motif profiles.
Z-score: Z = (N_real − ⟨N_rand⟩) / σ_rand. Significant if |Z| > 2.
Feed-forward loop (FFL): A→B, A→C, B→C — prevalent in gene regulatory networks.