Wait

Rests for one turn. This is most often used tactically for waiting a few turns. Serious resting should be done with the 5 command, for the sake of your keyboard and sanity. Resting is generally indistinguishable from any other action; healing, magic point restoration, etc, proceed at the same rate, whether you're resting or not. A few specific spells can be 'channeled' via the rest key for ongoing effects, as mentioned in their descriptions.

To wait is to pass one turn. It may be done by using the s or . keys. Waiting works like any other action (such as taking off and putting back on your weapon), though obviously does nothing. Waiting is required to continue the effects of spells like Searing Ray. Unless a status like Haste, Slow, or Statue Form modifies it, waiting lasts 1.0 decaAut.

Resting (with the regular 5 key) automatically waits until you regenerate health, MP, or find something interesting, like a monster. If you are at full HP and MP, it'll wait up to 100 turns.