From The Atlantic:

But Inglis’ statement was new. Analysts look “two or three hops” from terror suspects when evaluating terror activity, Inglis revealed. Previously, the limit of how surveillance was extended had been described as two hops. This meant that if the NSA were following a phone metadata or web trail from a terror suspect, it could also look at the calls from the people that suspect has spoken with—one hop. And then, the calls that second person had also spoken with—two hops. Terror suspect to person two to person three. Two hops. And now: A third hop.