It means that there is a dip in your neck. Basically, your neck is bent so that it resembles a bow, one that shoots arrows. The neck can become bent for many reasons; weather and string gauge come to mind. The typical fix for this is an adjustment of the truss rod. I wouldn't suggest adjusting it yourself, unless you are sure what a truss rod does.

I would take it to a music store and allow a technician to adjust it for you. It might cost a small fee, but it'll save you a bass and a headache.
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alright, a bit exagurated, but when you play your Bass neck, if your neck loks like it will be doing this shortly:
v strings

Then it be bowing.

then yea, get yoru truss rod reajusted, reajust if you know how to do it yourself, or take it in and what the guy above me said.