It's the addition of an alkyne to a halogen. It can be partial or total.
If you react an alkyne with 1 mol of Cl₂, for example, it'll be partial because only one pi bond will be broken and one Cl will attach to each of the carbons that had the double bond.
If you react the product of a partial halogenation with another mole of Cl₂, you'll no longer have pi bonds — only sigma ones.
It works like this: