Inert knowledge and inert skills are knowledge and skills that aren't transferred to new contexts. If you're capable of applying knowledge to new contexts it means you've understood.

Make it a habit of mind to take knowledge learned in one context and apply it to new contexts.

This habit of mind, applying knowledge, neutralizes this inertness, which is the most tenacious syndrome of school learning.

Understanding performance is thinking with one's knowledge and applying it in new contexts.

Applying knowledge is the ultimate understanding performance.