Digipak

Digipaks typically consist of a gatefold (book-style) paperboard or card stock outer binding, with one or more plastic trays capable of holding a CD or DVD attached to the inside.

Silver

A "silver CD" refers to how the data is transferred to the disc. If the bottom is blue/gold/green/etc (except in some special cases where a commercial release will be a gold CD) it's usually a CD-R, and anyone could make it. There are CD-Rs available with images printed on the artwork side of the disc using special printers, so that alone is not enough to discern whether or not it is a silver CD.

There are several ways to check whether a CD is silver-pressed or CD-R:
1) The most common and obvious way is to look at the bottom -- if it's any color other than silver (and occasionally gold for some special commercial releases), then it's definitely CD-R. But there are some CD-Rs that are silver-ish, so this alone isn't enough to say definitively that it's a silver-pressed CD.

2) Check for a matrix code printed onto the silver side of the CD around the center ring. Silvers will have this, while CD-Rs will have the matrix code printed on the inner-most ring (often made of plastic):

Here's a bit more reading on the difference between the two, although is mostly discussing official CD-R releases, rather than bootlegs:
https://www.discogs.com/forum/thread/344665