To understand the definition on trust here you have to understand how
encryption keys work. I would read the terminology section on the
[https://trisquel.info/en/wiki/email-encryption email encryption
documentation] for more info.
Here is a hypothetical scenario. Lets say one day I get an email from
someone and it says "Hey this is marioger from the Trisquel message boards.
Here is my GPG public key (XYZ) so now we can send encrypted emails." At
this point the key WILL work and we can send encrypted emails and I know the
emails I get came from the private key corresponding to (XYZ). But I don't
trust the key because all I have is someone who emailed me, sent me a key,
and CLAIMS to be marioger. Now, lets say then we meet in person and you
produce two forms of ID like a passport and driver's license (that say you
are marioger) and then tell me my key is (XYZ). At this point I probably
will trust that key (XYZ) does in fact belong to marioger.
Basically I could make an encryption key that says I am Barrack Obama or
George Bush. You shouldn't trust that unless you verify it. And this kind
of trust is trust in identity. It is different then "Here hold my wallet"
kind of trust.
So what it is saying is you are adding this PGP key from the PPA to your
system but at the current point in time it is untrusted in the sense that you
haven't verified where it came from.
