What it means: Black text is built using more than just black ink, but some combination of black, cyan, magenta and yellow. All black text should be built using only black, no additional colors.
Problems caused: Using more than one color to build black text can result in text that appears heavier and/or softer than intended. Normal, slight variations in registration of the 4 colors on press can cause other colors to show around the edges of the text that was intended to appear as black.
How to fix: Change the color of the text to 100% black.