梦寐以求 (mèng mèi yǐ qiú) is a set phrase meaning 'to have always dreamed of' — it describes a deep, positive longing for something you truly desire, like a goal or dream. Unlike 贪 (tān 'to covet, be greedy for'), which has a negative tone of excessive desire for money or pleasure, and 眼红 (yǎn hóng 'jealous, envious'), which is colloquial and focuses on resentment of others' success, 梦寐以求 is neutral or aspirational, often used for cherished ambitions.