Facebook – What are Story Impressions on Facebook apps

I don't think this is publicly available information otherwise it would be quite easy to know how and when to game the Translations on Facebook, in effect, a social hack.

For example, a few weeks ago, the Facebook Translation app had "sandwich maker" as a translation for female for l33t speak.

For future reference

I managed to add a custom tab by using this Facebook app. I was a bit confused because at first it asked me to use Facebook as me, so I though this surely isn't for a Facebook Page, but afterwards it asked me which Page I would like to add it to. So I selected my desired Facebook Page and that was it.

I'm a bit disappointed that nobody bothered to answer my question since it seems that this application is quite heavily used in Facebook community.