The “5.11″ in 5.11 Tactical is a reference to a class of climbing difficulty. More specifically, 5.11 is a specific ranking in the Yosemite Decimal System. YDS is a set of numeric ratings descrbing the the degree of difficulty in a rock climb. The “5″ in 5.11 refers to a class 5 climb, which is the most difficult possible. It is further divded into subclasses with “.11″ indicating a particularly challenging class 5 climb. At the time that the name 5.11 Tactical was coined a 5.11 climb was at the top end of the scale. Today, however, class 5 climbing contains 13 official subdivisions with 5.13 being the most advanced.