Are you considering returning to Final Fantasy XI? Be sure to read "Returning to Vana'diel"  our community collaborative guide! 
Areas · Missions · Quests · Coalitions · Assignments Reive · Skirmish · Delve · Incursion · Vagary · Sinister Reign 
Areas · Missions · Escha · Omen 
April Update Items  
Mog Garden · Monster Rearing · Monstrosity · Trust Magic · Unity · Ambuscade · Hard Mode Mission Battles · Master Trials  April Login Campaign  

Floor
To "floor()" something generally means that you drop the decimals after a certain point. This function seems to be applied at some stage to all expressions in FFXI. So, for instance, TP is floored. Damage calculations are floored, often in multiple places. Generally, and with the notable exception of TP, "Flooring" in FFXI means you drop all the decimals.
The Microsoft Excel version of this function, which follows the same formatting that people generally use with FFXI math, is formatted "floor(Number or Expression, Significance)"
Number or Expression would be the value that you want to limit to a certain number of decimal places, and Significance is that number of decimal places. Because FFXI seems to default to dropping all the decimals, if you don't see a "Significance" you can assume it to be 1 (dropping all the decimals).
Examples:
 floor(4.56, 0.1) = 4.5
 floor(5×1.31, 0.1) = 6.5
 floor( (176+190)*(130%), 1.0) = 256