Definition 3.4 ([...]) Two (sets of) nodes 𝑋 and 𝑌 are d-separated by a set of nodes 𝑍 if all of the paths between (any node in) 𝑋 and (any node in) 𝑌 are blocked by 𝑍
Source: Pearl (1988), Probabilistic Reasoning in Intelligent Systems: Networks of Plausible Inference