伪 is a bound morpheme (cannot stand alone as a word) that functions like a prefix meaning 'false, fake, pseudo-'. It appears in compounds such as 伪造 (to forge), 伪劣 (fake and inferior), and 伪政权 (puppet regime). Unlike the standalone adjective 假 (fake), 伪 is always attached to another character and often carries a more formal or political nuance.