It means changing software as quickly, cheaply (economically), and securely as possible. It involves having the necessary tools, data, and capabilities to monitor and optimize technical components and the digital workplace.
Technical Agility enables organizations to identify gaps or optimization opportunities in their systems and software. It's part of the Five Dimensions of Enterprise Agility (Cake Model) and Leading Exponential Change, initially published in 2018. It is also part of the Enterprise Agility Framework.
For more detailed information about them, check Enterprise Agility Fundamentals, Chapter 2, page 94.