Is the human ovum visible to the naked eye?
The line that you quote from the Wikipedia page is talking about ova in general, whereas your question relates specifically to human ova. The "Human and mammal ova" section of the same article states that 


  The ovum is one of the largest cells in the human body, typically
  visible to the naked eye without the aid of a microscope or other
  magnification device.


With the stated average size of 0.12 mm in diameter (same Wikipedia article), an ovum is very, very small, but presumably a person can still see it unaided.