Abbreviation of 阿兰若 (ālánrě), a transliteration of Sanskrit araṇya 'forest, wilderness' — i.e. a place of quiet practice away from settlements. In Tang poetry it's a stock setting; pinyin is irregular: 若 here is read rě, not ruò.
culture
Famous in pop culture as the haunted temple 兰若寺 (Lánrě Sì) of 倩女幽魂 ('A Chinese Ghost Story', 1987 film), which itself draws on 蒲松龄 (Pú Sōnglíng, 'Pu Songling')'s Qing-era 《聊斋志异》.
