From Dictionary.com :
Errata - a list of errors and their corrections inserted, usually on a separate page or slip of paper, in a book or other publication; corrigenda.
In this case, a card has incorrect text, usually due to a translation error. Pokemon needs to correct the error. It is not feasible to retrieve each and every copy of the card and reissue them with that corrected text. So they issue a statement saying, in effect; "This card has incorrect text. Here is the text as printed and here is the correct text. Treat this card as if it has the correct text going forward".
All players and staff are responsible for being aware of errata.
Team Compendium makes this relatively easy for players by collecting ALL Pokemon errata in one place for you, in the errata section of the Compendium. Many errata never see corrected versions in print. Great Ball is an exception in that regard. However, the errata still exists and so players are responsible for being aware of it.