Leading lines in photography are existing lines within the frame of a photograph which the photographer has deliberately aligned/arranged (prior to taking the photo) by adjusting their composition either shifting their body or camera. It should result in lines which “lead” to the subject, increasing the focus of the viewer, allowing for a more enjoyable viewing experience.
It is often paired with the rule of thirds although not necessarily.
Since I started photographing London (back around 2008), I have made a conscious effort to practice and master this as it greatly improves photographs, their impact, and the ease with which a viewer will appreciate your work, a certain user experience I guess.
I include some examples of my London photography so you can see for yourself the importance of leading lines in photography.