Hoplites were the heavily armed infantry. They wore helmets, breastplates, and leg armor made of bronze. In addition, they possessed a swords and spears. Their armor allowed them to withstand attack by arrows. On the negative side, though, they were much slower moving than the lightly armed infantry, which posed a major problem if required to make a hasty retreat or assault.
Athenian citizens who were not able to maintain horses but could afford their own armor were required to be hoplites. That's right, unlike today's army you had to buy your own equipment! The fact, then, that Socrates was a hoplite suggests he wasn't always poor. Apparently, his dedication to philosophy over and above material concerns gradually led to his impoverishment.