Status effects are conditions that alter your character. Whether brought on by a monster ability, spell, quest, or item, these change how you interact in the world of Final Fantasy XI. The following information is taken directly from the FFXI online Game Manual:
If your character's status changes, such as being poisoned in an enemy attack or using an ability to increase your attack power, it will be reported in your log window and an icon will appear at the top center of the screen. There are various icons used to indicate the different types of status effects. To view the details of a given icon, press the Δ button on the DUALSHOCK®2 analog controller, the Y button on an Xbox 360 controller, the + key on your keyboard's numeric keypad, or f key on compact keyboard twice and move the cursor over the icon. An explanation of the icon will appear in the upper window. If a status effect wears off, it will be reported in your log window, and the icon will disappear from the top of the screen.
With the exception of Boost, status effect duration timers are paused while in dialogue with an NPC.
These status effects can be separated into three distinct groups: