3rd lumped circuit abstraction postulate
At high frequencies, you need to model connections between elements with a transmission line as there are delays associated with the interconnects. This is what you are referring to. At low frequencies, these delays are negligible to the operation of the circuit as a whole as they act at very small timescales, but at higher frequencies the behaviour of the circuit needs to take these delays into account as they cause reflections and unexpected noise into the circuit if it is not designed properly.

For more information check out wikipedia's article on Transmission lines