A universally closed morphism is a morphism 
of schemes such that every
base change 
is a closed
map.
Universal closedness is preserved by composition and base change. Every proper morphism is universally closed.
Universally Closed Morphism
See also
Base Change, Closed Map, Fiber Product, Morphism, Proper MorphismExplore with Wolfram|Alpha
References
Grothendieck, A. and Dieudonné, J. "Éléments de géométrie algébrique. II. Étude globale élémentaire de quelques classes de morphismes." Publ. Math. IHES 8, 5-222, 1961. https://doi.org/10.1007/BF02699291.The Stacks Project Authors. "Valuative Criterion for Universal Closedness." §26.20 in The Stacks Project, Tag 01KB, 2026. https://stacks.math.columbia.edu/tag/01KB.Cite this as:
Weisstein, Eric W. "Universally Closed Morphism." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/UniversallyClosedMorphism.html