As Robin says, it's all about perspective, and the fact that lines will tend to diverge — or actually, more like converge, but it all depends on which way round you consider it.

In photography, especially when attempting to photograph tall buildings from ground level, we always come up against the problem usually referred to as 'converging verticals' (though of course, as Robin says, it applies equally well to horizontals!)

In the 'olden days', 'technical cameras' were used to correct this effect, but now it is amazing the results that can be obtained by digital image manipulation.

Le terme correct, en français, est plutôt "ligne de fuite". Dans mon dictionnaire, je trouve cette traduction... A vous de juger, l'anglais n'est pas ma langue maternelle.