1. Noun. (analysis) In the space \mathbb{R}^n, the metric d(\vec x, \vec y) = \sqrt{(x_1 - y_1)^2 + (x_2 - y_2)^2 + ... + (x_n - y_n)^2} where \vec x = (x_1, ..., x_n) and \vec y = (y_1, ..., y_n). ¹
¹ Source: wiktionary.com
