Chloramine is the name of the chemical that forms from the combination of chlorine and organic matter. It is commonly used as a disinfectant, but can occur as an unintended reaction of chlorinated water and organic matter: at a swimming pool, in packaged lettuce rinsed with municipal water (commonly disinfected with chlorine), etc. There are three types of chloramines: monochloramine, dichloramine, and nitrogen trichloride. The last of these can be particularly troublesome at poolside - it is hydrophobic and readily leeches out into the air from the pool water, thereby exposing attendants and other poolside workers.
Chloramine gas is the active agent in the toxic fumes formed when bleach (NaOCl) is mixed with ammonia (NH3). Both monochloramine (NH2Cl) and dichloramine (NHCl2) gas form from this reaction. When inhaled, these compounds break down into ammonia, hydrochloric acid (HCl, the same acid used by humans for digestion) and oxygen free radicals. These compounds cause severe irritation of the lung tissues, and exposure to this gas can be fatal if one is exposed to it at a high concentration or in an area with restricted ventilation. A mild exposure, such as that resulting from cleaning a litterbox (with ammonia-bearing cat urine) with bleach, will cause only minor respiratory tract inflammation (thus speaks the voice of personal experience). Of course, unless you like the feeling of a freshly irritated respiratory tract, unnecessary exposure should be avoided.
Chloramine is used to disinfect city water by means of injection of ammonia and bleach into by the municipality's supply. The toxicity of this compound can be a concern when using tap water for pet fish. If let stand, it takes 2-5 days for the chloramines to dissipate. (Chlorine will evaporate out in 24 hours.)