The family of chemicals called “halogens” include bromine, chlorine, fluorine and iodine, among others. The term “halogen” means they are all in the same column on the periodic table of the elements (if you’re interested, see col. 17 on the right-hand side of the table). Notice all four chemicals are good cleaners. These solvents are used for all sorts of precision cleaning applications. They can be used to remove fluxes from circuit boards or to degrease tiny metal parts. They rinse away particulate and they also can be used to deposit coatings and lubricants. It is an incredibly versatile group of chemicals.
Special note: Some companies and countries have restrictions on the use of halogens in fluxes or solder pastes that might remain on PCBs after manufacturing. While the details vary by region, in general no MicroCare halogenated cleaner remains on the board (they are all 100% volatile and evaporate away) so they are in compliance with the no-halogen restriction.