Sentence:  The point where a family of parallels appear to meet is called their “vanishing point” by artists, and their <WSD>"point at infinity</WSD>" by mathematicians. The horizon itself, which consists of all the <WSD>points at infinity</WSD>, is called the "line at infinity". 
Meaning of the word marked with <WSD> tags:  An asymptotic point in 3-dimensional space, viewed from some point, at which parallel lines appear to meet and which in perspective drawing is represented as a vanishing point.