Help with Dates...

Would someone be so kind and explain how the Norwegian dates work? For instance what is "Trin or Trinit" mean? I have found another ancestor, Anne Sophia Nielsdatter (b. 1782 Rakkestad, Ostfold )- on page 28 at: http://www.arkivverket.no/URN:kb_read?uid=20998&urnread_imagesize=gigant&show=18#bunnen - and I don't know the month she was baptised. It looks like it was on the 7th of ?? 1782[?] Thanking you in advance for any help! J. Jensen