Jay Bilas wrote a landmark article "Toughness" and then an eponymous book.
To me "Toughness" has a lot in common with 'professionalism,' a willingness to "get after it," even when you're tired or not at your best.
Toughness means knowing what to do, how to do it, when, and why you do it.
Tough players block out, take charges, fight through screens, move without the ball, set great screens, get the 50-50 balls, and constantly work to improve.
Tough players appear on time, mentally, and physically ready to play.
Coaches can help players develop a degree of toughness, but ultimately the player determines her toughness level. As youngsters, my twin girls played every day with a pair of brothers...rough play. A random fan approached me once and said, "I love how your daughters play, just like boys." I'm convinced those pre-school play sessions did that.
Being called a tough player by a coach or teammate is one of the highest compliments you can get. Conversely, the "S - word" (soft) stands as a major indictment of your play.
Toughness translates passion and love for the game into action, playing the game smart and hard and unselfishly. Tough teams communicate on the floor but can share silence in the team room before the game.
Here's a brief excerpt from Bilas' article:
I often wonder: Do people really understand what coaches and experienced players mean when they emphasize "toughness" in basketball?
Toughness has nothing to do with size, physical strength or athleticism. Some players may be born tough, but I believe that toughness is a skill, and it is a skill that can be developed and improved. Michigan State coach Tom Izzo always says, "Players play, but tough players win."