According to some webpages, the naginata was generally used by non-mounted samurai (ashigaru, or peasant-soldiers, more often used yari, the spear). Of course, the sasmurai also wore the two swords. Women were also samurai. They were expected to manage the household, and defend it as necessary. Women were primarily instructed in tanto use, but were also taught the sword and naginata. The naginata was also ideal for castle defense.
And now you know!