cereal / serial are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
cereal: (noun) grass whose starchy grains are used as food: wheat; rice; rye; oats; maize; buckwheat; millet. (noun) a breakfast food prepared from grain. (adjective) made of grain or relating to grain or the plants that produce it.
serial: (noun) a serialized set of programs. (adjective) pertaining to or composed in serial technique. (adjective) pertaining to or occurring in or producing a series. (adjective) of or relating to the sequential performance of multiple operations.
cereal: s·IH·r·iy·ah·l
serial: s·IH·r·iy·ah·l
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)