In chemistry, a transition metal is a chemical element in the d-block of the periodic table, though the elements of group 12 are sometimes excluded. Wikipedia

Either an element whose atom has an incomplete d sub-shell, or any element in the d-block of the periodic table Wikipedia Disambiguation

Series of chemical elements Wikidata

One of a group of metallic elements in which the members have the filling of the outermost shell to 8 electrons interrupted to bring the penultimate shell from 8 to 18 or 32 electrons; includes elements 21 through 29 (scandium through copper), 39 through 47 (yttrium through silver), 57 through 79 (lanthanum through gold), and 89 through 112 (actinium through ununbium) on. OmegaWiki

A transition element. Wiktionary

Transition element. Wiktionary (translation)