As described in the Basic Information section the strong typically refers to the bottom half of the blade including the Schilt. Sometimes translated as "forte", the strong of the blade is slow moving but has great mechanical advantage.
This is neither a positive or negative trait, it is simply the nature of the way swords work. The strong of the sword is slow moving compared to the tip. If we imagine the sword as the spoke of a wheel it is easy to see that the tip travels a much greater diameter in the same time interval as the schilt, and this is reflected in the agility of the strong. The strong effectively moves close to the speed of the hands, but at the same time, being so close to the hands and body it can be used with great strength.
When using the weak we should consider these traits to make the most of our techniques. Typically, for example, we parry with the Strong, as well as carry out wrenching techniques, while we deceive and change through with the Weak.
Related to weak is the concept of being Hard in the bind.