My friend got a PTR-91 and I was wondering; What the fuck does

You could have posted this in a QTDDTOT

You could have just Googled this

But you didn't

So now I laugh

Shoulda googled it, I did and it took like 3 seconds:

S = Sicher ((tsichaar) 'Safe'
E= Einzelfeuer-- (Ine-tsell-foyer) Literal translation is 'single fire'. Semi-auto in English.
F= Feuerstoß (pronounced foyer-schtoss) The letter that looks like a capital B is called an ess-tset and pronounced like a double 's'. Literal translation is 'burst fire' or full automatic in English.

This translation would not be complete without the 'informal' English translation:

S= Safe
E= Economical
F= FUN!

Little known fact, ptr-91's are made in mexico, so it stands for "el shooto"

eh, i prefer to ask on /k/ more reliable than google desu.

the E stands for eins wich is German for one. and in related news OP is a faggot for wasting space on the board with this tread instead of using QTDDTOT