Shukla Poornima is the name for the 15th Tithi (Full Moon lunar day). It's the 15th Tithi of Shuklapaksha. It's nature is Saumya Prada, which can be interpreted as "one that bestows soberness and clarity". It's good for following works: all Manglik (auspicious) works; religious rituals; peaceful and Paushtik works, Pratishta, temple, marriage, painting, sculpture, art, ornaments, house, war. Sex, oil massage and Upanayana are strictly prohibited.
Chandra is a Devata which rules Poornima (referring to Muhurta Chintamani and Poorva Kalamrita). All activity that's somehow related to Chandra (Manas, consciousness, clarity of mind, mother, meditation, etc) is very auspicious during this day. According to Brihat Samhita, Pitri rule Poornima. Pitri are spirits of the departed ancestors and there are lots of Pitri forms and classes (devāḥ pitaraḥ, manuṣyāḥ pitaraḥ, etc). The main idea for Poornima (again according to classical Brihat Samhita) is that Pitris should be honored during the 15th lunar day.
Being Poorna (that can be translated as "full", "complete" or "perfect") and ruled by Guru (Jupiter), 15th Tithi of Shuklapaksha is suitable for following works: marriage, Manglik deeds, travelling, tourism, pilgrimage, coronation, peaceful & Paushtik works.
If Shukla Poornima prevails at the time of Sun's ingress into siderial sign then it's called Parva Tithi (lunar day for festivals) and should be avoided in all auspicious elections.
During vedic months Chaitra, Jyaishtha, Ashada, Kartika and Phalguna Shukla Poornima becomes Manvadi Tithi, which is considered to be extremely auspicious for any Punya Karma (Japa, Tapa, Dana, Havan, Homa etc.). The names of these Manvadi Tithis respectively are: Swarochisha, Vaivaswat, Tamas, Ottama and Savarni. However, these days should be avoided in such elections as starting of education, marriage, ending of fasts, construction of house & entering thereof, travelling and plantation.
NB! There're no Tithi Shoonya Lagnas, Nakshatras or Maasa for Shukla Poornima as well as Dagdha Rashi (Rashi that burns Tithi when Surya (Sun) is in it during Poornima) that makes it extremely auspicious day for any activity (taking into consideration pre-cautions mentioned above).
