Cetrimonium chloride is a quaternary ammonium salt. Its concentration in cosmetics is highly controlled by state regulations. It's similar to another conditioning ingredient, behentrimonium chloride with only the number of carbon atoms they contain being the main difference, which slightly changes the feel of the conditioner on the hair when you apply it.
It's an anti-static, conditioning ingredient that helps keep hair looking and feeling smooth. It also acts as a preservative by preventing the growth of bacteria in liquid solutions, so products last longer. It's partly water-soluble and partly oil-soluble, so oil and water become dispersed and give products a good consistency and a gentle cleansing foam.