text: what is wikipedia? collaborative encyclopedia, education community on-line, the greatest world free encyclopedia you've already answered it yourself. :^)  it is probably the greatest single organized repository of all human information ever known.  what makes it great is that anyone can contribute but anyone can also correct, edit, or flag problems with the information in any article.  i dare say that many articles have many more people review them and improve them than any other encyclopedia on the planet.  it would appear that many contributors are professional experts in their fields.  on the topics of math, i've found much better, more comprehensive information than you can find in many books.