puzzled by Pattern Solution 2nd sentence

"Definition: Pattern Solution

A Pattern Solution of Graph Pattern GP on graph G is any substitution S
such that GP matches G with S.

For a graph pattern GP formed as a set of triple patterns, S(G), has no
variables and is a subgraph of G."

The first sentence is fine (I've transcribed it in MathML and
converted it via XSLT to N3). I can't make out the 2nd
sentence, though. Help?

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E