Nitrate is an ion, NO3- to be precise. It is, (simplistically), the end result of your biological filtration. The fish produce toxic waste in the form of ammonia, highly toxic, this gets converted to slightly less dangerous nitrite, which gets converted to nitrate. Thus, if you have a well functioning filter system, you should see no measurable ammonia or nitrite, and a level of nitrate.
You can measure your ammonia/nitrite/nitrate levels with test kits from your lfs, they may even do it for you.
Can any one tell me what nitrates are. I have been keeping arrican cichlids for about 2 years, with no problems. But some one from the cichlid forum was pretty rude cause I didnt know what they were.And all my fish are fine. I hope? Please help. 
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