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'''Quiescent Nodes''' are [[Node|nodes]] at [[Depth|depth]] zero or below, where a [[Quiescence Search]] is performed <ref>[http://groups.google.com/group/rec.games.chess.computer/browse_frm/thread/926eaf0869b6f176# quiescent vs non-quiescent node counting] by [[Robert Hyatt]] from [[Computer Chess Forums|rec.games.chess.computer]], July 01, 1996</ref> <ref>[https://www.stmintz.com/ccc/index.php?id=387518 Re: simple node definitions question] by [[Robert Hyatt]], [[CCC]], September 13, 2004</ref>. The most top subset of quiescent nodes at depth zero are also called [[Horizon Node|horizon nodes]]. If the quiescent node is an expected [[Node Types#CUT|Cut-Node]], that is the evaluated [[Quiescence Search#StandPat|standing pat]] score is already greater or equal than [[Beta|beta]], the quiescent node becomes a [[Leaf Node|leaf]] with the [[Lower Bound|lower bound]] score of beta ([[Fail-Hard|fail-hard]]) or the stand pat score ([[Fail-Soft|fail-soft]]). Otherwise, winning captures (or checks) may either cause a [[Beta-Cutoff|beta-cutoff]] or raise [[Alpha|alpha]] with an [[Exact Score|exact score]] at [[Node Types#PV|PV-Nodes]]. At expected [[Node Types#ALL|All-Nodes]] with evaluated score (far) below alpha, if no [[Tactical movesMoves|tactical move]] is available, or due to [[Delta Pruning]] good enough to raise alpha, those [[Leaf Node|leaves]] return alpha ([[Fail-Hard|fail-hard]]) as an [[Upper Bound|upper bound]]. This may also appear, if this quiescent node was not a leaf, since some captures were not pruned, but tried without raising alpha.