What is allylic halogenation\[?\]

Hint: First we know In chemistry, halogenation is a chemical reaction that involves the addition of one or more halogens to a compound or material.. Then we have to know about halogenation. Then we write what is allylic halogenation by replacing halogen to the compound at the allylic position.

Complete answer:
Halogenation is the replacement of a hydrogen atom by a halogen atom in a molecule. The pathway and stoichiometry of halogenation depends on the structural features and functional groups of the organic substrate, as well as on the specific halogen.
 The product resulting from halogenation will have quite distinct properties from the start compound. When you have an alkene in the presence of a halogen you can add a halogen to the compound at the allylic position instead of adding it on the double bond. It undergoes a radical chain mechanism (Initiation, propagation, termination). Because we substitute
(=replace) one of the hydrogen-atoms by a halogen-atom. Halogen may be fluorine, chlorine, bromine or iodine.
Typical reaction is
\[C{H_4} + C{l_2} \to C{H_3}Cl + HCl\]
Where one of the \[Cl - \]atoms is used to take an \[H - \]atom away from the molecule, and the other one is taking its place.
Usually, this takes heat and pressure. Is the halogenation of an alkane (a substitution reaction).

Note:
Note that halogens is the group name that is given to fluorine, chlorine, bromine and iodine. Since these elements have very similar behaviour, they are often treated as a group. The term 'halogenation' can thus refer to replacing any number of hydrogen atoms with each and any of the members of the group.