Compare a catalysed reaction with an uncatalysed reaction

Catalyzed means there is some "other" chemical or surface around which happens to provide a short-cut for the reaction, so it can happen faster or at lower temperature. Uncatalyzed is doing it the hard way, so it usually requires higher temperatures to get going well enough. Sometimes those temperatures are enough higher that the chemicals break down (have undesired reactions and produce the "wrong" products).