五角星，又称五芒星，是指一种有五只尖角，并以五条直线画成的星星图形。英文「五角星」（pentagram）一词出于希腊语「πεντάγραμμος」（pentagrammos）或「πεντέγραμμος」（pentegrammos）的名词形式「πεντάγραμμον」（pentagrammon），原意大概是「五条直线的」或「五条线」。而中文「五角星」的意义则显而易见，指有五只角的星形。然而，中文「五角星」不一定指本文所谈论的「标准」五角星。中文「五角星」一词有时亦泛指所有有五只角的星形物。

本文以下所讨论的五角星是指「标准」五角星。即正五角星。

A pentagram (sometimes known as a pentalpha or pentangle or a star pentagon) is the shape of a five-pointed star drawn with five straight strokes.

The word pentagram comes from the Greek word πεντάγραμμον (pentagrammon), from πέντε (pente), "five" + γραμμή (grammē), "line". The word "pentacle" is sometimes used synonymously with "pentagram" The word pentalpha is a learned modern (17th-century) revival of a post-classical Greek name of the shape.