Boston Suspects Are Seen as Self-Taught and Fueled by Web

[Pholus]

20. Really. See the definition that is actually used....

refers to the tactics, not the head count. A "lone wolf" acts without material support from outside groups, without orders coming from a command structure and without personal contact with the group with which they identify. That makes them hard to catch by classic law enforcement techniques (since they work by watching who is talking to who through surveilance).

To continue cribbing from Wikipedia and adding the emphases...

According to the Anti-Defamation League, the term "lone wolf" was popularized by white supremacists Alex Curtis and Tom Metzger in the 1990s. Metzger advocated individual or small-cell underground activity, as opposed to above-ground membership organizations, envisaging "warriors acting alone or in small groups who attacked the government or other targets in 'daily, anonymous acts.'"[1] He referred to these warriors as "lone wolves".

Now in the U.S. both Timothy McVeigh and John Allen Muhammad were both deemed classic examples of lone wolves by law enforcement. Neither acted completely alone. I seem to remember both had helpers (Terry Nichols and Lee Boyd Malvo).