Atomic specrum is the EM wave pattern obtained on a screen due relese of EM wave during de-excitation of an electron in an atom

It is basically of 2 types :-

1. Emmission spectrum -> when the atom emits the EM wave and it is directly made to give pattern on the screen, it is called emission spectrum. These are those waves which are actually emmitted by the atom.

 

2. Absorption spectrum -> when a mixture of EM waves is passed through the sample of substance. It absorbs all those waves which can excite it's electrons.

Rest of them will pass through it and give pattern on it. This is the absorption spectrum.

            Both these specra are negetive copy of each other i.e. if there is a region of bright light in the former, ther will surely be dark portion in that area in latter.