HELP! What does 'Trusted' files in the Scan Log refers to?

Hi Guys,

I am using the Symantec "Virus and Spyware Protection" Custom Scan.
And couldn't figure out what's the column 'Trusted' means? Which appears in the Scan Log.
I feel strange cause the number of Infected files and Trusted files are sometimes different.
Such as there was a scan that shows 2 Infected and 3 Trusted files.
And in the Risk Log there are 3 files shown infected but one of them is a compressed file which has the same path as the other file. But I assume it as there are only 2 viruses. :x

Greatly appreciate if anyone could clear my doubts. And pardon for my bad English.

Thanks, Viola.

Have a nice day:D