It was for an extra race that was set to take place somewhere in Europe, but Bernie just confirmed that this years calendar will only feature 19 races so that race date is obviously cancelled now. The race that previously occupied that slot was the race at Valencia that will now alternate with Catalunya starting this year.
Edit: Just some additional info - Bernie wanted to have the Turkish GP come back this year (and it was essentially the only track he was willing to add for this year) but the government was not willing to invest in the track again so the deal fell through.
BBC are covering this cancelled race! ACE!!