Dear Aspirant

Transition elements (also known as transition metals) are elements that have partially filled d orbitals. IUPAC defines transition elements as an element having a d subshell that is partially filled with electrons, or an element that has the ability to form stable cations with an incompletely filled d orbital .

In general, any element which corresponds to the d-block of the modern periodic table (which consists of groups 3-12) is considered to be a transition element. Even the f-block elements (https://byjus.com/jee/f-block-elements/) comprising the lanthanides and the actinides can be considered as transition metals.

However, since the f-block elements have incompletely filled f-orbitals, they are often referred to as inner transition elements or inner transition metals

All the best