There are several differences between monocots and dicots, here are three big ones. The main one (that gave rise to the names) is that monocots have seeds that are one piece (like corn), while dicot seeds can be easily split in half (like peas). Other differences include that monocots have flower parts (like petals) in multiple of threes while dicots usually have them in multiples of 4 or 5. In terms of the leaves, monocots exhibit parallel veins while dicots have reticulated (net-like) veins.
