How to consider a line as Transmission Line

How to consider a line as a transmission line? If it is is based on the frequencies we use; then is the connections inside the CPU of a computer can be considered as one?

All conductors are transmission lines. When they are very short compared to a wavelength or compared to a pulse rise time they can be accurately approximated as an ordinary connection without considering the reflections and impedance transformation effects.

A rule of thumb demands to consider transmission line properties of a connection if the electrical length is larger than 1/10 of wavelength.