昌 (chāng) is a bound morpheme (not an independent word) meaning 'flourishing; prosperous'. It appears in formal or literary compounds, most commonly 昌盛 (chāngshèng, 'prosperous') and the set phrase 繁荣昌盛 (fánróng chāngshèng, 'prosperity and flourishing'). You will not encounter it alone in modern spoken Chinese—it always attaches to another morpheme. Think of it as a 'building block' for describing thriving states of a nation, city, or age.