What do you mean by 'inner-transition elements'?

Explanation

Inner transition elements are those which connects 's'-block and 'd'-block. In between '6s' level and '5d' level '4f(14 elements) belongs. The electronic configuration is `ns^2 (n-1)d^(0-1) (n-24)^(1-14) these are rare earth metals. '4f' elements are called Lanthanides. '5f' elements are called Actinides.