A spider typically has eight legs. Those legs are arranged as four pairs on the front body section, called the cephalothorax, and are one of the clearest features separating spiders from insects.
Spiders belong to the class Arachnida, along with scorpions, ticks, mites, and harvestmen. Adult insects generally have six legs, while adult arachnids usually have eight. Spiders also lack antennae and have two main body regions rather than the three typical of insects.
A spider's legs are jointed and contain seven main segments, including the femur, tibia, metatarsus, and tarsus. They help with walking, climbing, hunting, sensing vibrations, and handling silk. The small appendages near the mouth are pedipalps, not an extra pair of legs; in males, they also play a role in reproduction.
The word "typically" matters because damaged or developing spiders may appear to have fewer visible legs. Some other arachnids can also confuse observers: certain species use leg-like appendages for sensing or feeding, but a normal adult spider has four pairs of walking legs.