<unk>  is a chemical reaction that incorporates a halogen atom into a molecule.  More specific descriptions exist that specify the type of halogen: fluorination, chlorination, bromination, and iodination.
In a Markovnikov addition reaction, a halogen like bromine is reacted with an alkene which causes the π-bond to break forming an haloalkane. This makes the hydrocarbon more reactive and bromine as it turns out, is a good leaving group in further chemical reactions such as nucleophilic aliphatic substitution reactions and elimination reactions
Several main types of<unk>  exist, including:
Free radical<unk> 
Ketone<unk> 
Electrophilic<unk> 
Halogen addition reaction
Specific<unk>  methods are the Hunsdiecker reaction (from carboxylic acids) and the Sandmeyer reaction (arylhalides).
An example of<unk>  can be found in the organic synthesis of the anesthetic halothane from trichloroethylene which involves a high temperature bromination in the second step :
Halogenation
Sterilization 
Detoxification
Induction heating
Freeze drying
Transmetalation
Carboxylation
Electrolysis