In the past, Apple has used the Moscone West facility as a location for their popular WWDC event. The calendar listing is for an unnamed event with the tag of convention/tradeshow. Apple is not mentioned anywhere, but the timing and the location make sense.
WWDC is where Apple makes huge announcements, such as new versions of their popular iPhone. That has been the case for the last few years, so it is safe to assume that the iPhone 5, or whatever they decide to call it will be unveiled during this event. Tell us what you think in the comments below.
source: Into Mobile