i should know

You have fish in your tank and aren't aware of what cycling a tank refers to? Rut roh.

It refers to establishing the beneficial bacteria in a fish tank. There are multiple ways of doing this and I feel the most humane ways are fishless.
 
There's a sticky thread on cycling in the Freshwater Newbie forum, I suggest you read it before you add any more fish. Unless you're trying to cycle the tank as a brackish tank, there's a sticky in this forum for that (by sploke)
 
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