Halogen addition:

The reaction of an alkene along with a halogen like bromine or chlorine results in the creation of a vicinal dihalide. The halogen molecule is split and after that the halogens are added to each end of the double bond as shown in below figure. Vicinal dibromides are helpful in the purification or protection of alkenes as the bromine atoms can be removed within different reaction conditions to restore the alkene. Vicinal dibromides can as well be converted to alkynes.

Figure:  Electrophilic addition of bromine to 2, 3-dimethyl-2-butene.