Hari uposatha (Pali; Sanskerta: उपवसथ, upavasatha; KBBI: uposata) merupakan hari-hari bagi pengikut Buddhisme untuk melakukan perenungan dan pengamatan yang sudah dilakukan sejak masa kehidupan Buddha Gotama dan masih dipraktikkan hingga hari ini.[1][2]Sang Buddha mengajarkan bahwa hari uposatha diperuntukkan "membersihkan pikiran dari hal-hal kotor," yang menyebabkan ketenangan batin dan kebahagiaan.[3] Pada hari uposatha, umat awam (upasaka-upasika) dan para biksu-biksuni secara intensif akan berlatih ajaran Buddha dan memperdalam pengetahuan mereka. Selain itu, umat awam beraliran Theravāda juga dianjurkan untuk mengamalkan Astasila (Pali: Aṭṭhaṅgasīla), termasuk di dalamnya aturan untuk berpuasa dari tengah hari sampai matahari terbit (aturan keenam), penghindaran diri dari berbagai jenis hiburan (aturan ketujuh), dan penghindaran diri dari segala jenis aktivitas seksual (aturan ketiga). Umat awam yang beraliran Mahayana menjalankan aturan berpuasa daging dengan menjalankan praktik vegetarian.
^For a description of the contemporary practice of the Uposatha in Thailand, see Khantipalo (1982a), which is also excerpted in this article below.
Kariyawasam (1995), ch. 3, also underlines the continuity of the ancient uposatha practice in Sri Lanka: "The poya [Sinhala for uposatha] observance, which is as old as Buddhism itself, has been followed by the Sinhala Buddhists up to the present day, even after the Christian calendar came to be used for secular matters. Owing to its significance in the religious life of the local Buddhists, all the full-moon days have been declared public holidays by the government."
^The uposatha day is sometimes likened to the Judeo-Christian notion of the Sabbath. Pali English dictionaries that define "Uposatha" as "Sabbath," are Buddhadatta (2002), p. 63, and, and PED(Rhys-Davids & Stede,1921-25), p. 151.
For an example of the Uposatha being equated with Sabbath by a modern Buddhist master, see Mahasi (undated), p. 2, where he writes: "For lay people, these rules [of discipline] comprise the eight precepts which Buddhist devotees observe on the Sabbath days (uposatha) and during periods of meditation." Harvey (1990), p. 192, also refers to the uposatha as "sabbath-like."