What does "application" refer to here?
"Application" here means "use," "usage," or "implementation." Steve Jobs is saying that his practice of calligraphy had no "practical application" in his life, meaning that despite being interesting and fun, unfortunately, it held no practical use or value. Ex: The program is designed to be applicable across different settings and contexts. Ex: I am learning coding. Although I cannot apply my knowledge to work, I still enjoy the process of learning.