What Is The Difference Between An Insect And An Arthropod?

The arthropods are are large group of invertebrates that include the subgroups, the Arachnida, (the spiders, ticks and mites), on the Chilopoda, (the centipedes), the Diplopoda (the millipedes) and on the Insecta (the insects). Insects include flies, wasps, bees, beetles, dragonflies, butterflies and moths, amongst others.

Insects have three body regions: head, thorax, and abdomen. The head picks up information about the outside world and also houses the mouthparts. Insect use different techniques to eat and they munch their way through all sorts of different foods, so mouthparts vary widely between species.  The thorax provides support for the three pairs of legs and, if they have them, for one or two pairs of wings. The abdomen carries out digestion and reproduction.

The body of a spider has two parts: a cephalothorax (a fused head and thorax)
and an abdomen. The two separate parts are connected by a narrow waist. The upper side of the spider is called the dorsal side and the bottom is called the ventral side. The dorsal side of cephalothorax is made of chitin and is called the carapax. The back the cephalothorax is just called the thorax.

Insects is a category of Arthropod. Arthropod is a wider range of animal kind that includes the insects, arachnids, crustaceans, and others. For more information visit the following link.
Arthropod

The insect has 3 body parts and six legs and they can fly. The Arthropod has 2 body parts and they have eight legs.