Transition metals are those elements which consists of atoms which has partially filled d-orbitals or sub-shells or which gave rise to cations with an incomplete d-orbitals or sub-shells.
d-block elements are called transition metals which includes group 3 to 12 in the periodic table.
However, f-block elements known as Lanthanoids and Actinoids are also considered as transition metals generally known as Inner Transition metals.
The most common well known transition elements are Copper, Iron, Manganese, Gold, Silver, Mercury, Cobalt, Titanium, etc.