What is emission line spectrum?

When an atom is heated the electrons jump to higher energy levels. Eventually they drop back down one or two or three levels emitting light energy. Each jump has a distinct package of energy and hence wavelength and thus produces a single line of the spectrum. A sodium street light is orange because it has two very strong orange lines as well as some fainter ones.

Uses of emission line spectrum are scientists use emission spectra to confirm the presence of an element in materials of unknown composition