1. The property of being big and strong
   "The ruggedness of the terrain challenged even the most experienced hikers";
   - huskiness, toughness
    
2. The quality of being topologically uneven
   "the ruggedness of the mountains"
    
3. The quality of being difficult to do
   "the ruggedness of his exams caused half the class to fail";
   - hardness

Type of: difficultness, difficulty, strength, unevenness, variability