Deltiology (from Greek δελτίον, deltion, diminuitive of δέλτος, deltos, "tablet, letter"; and -λογία, -logia) is the study and collection of postcards. Compared to philately, the iden- tification of a postcard's place and time of production can often be an impossible task because postcards, unlike stamps, are produced in a decentralised, unregulated manner. For this reason, some collectors choose to limit their acquisitions to cards by specific artists and publishers, or by time and location.
Lake Sfânta Ana (English: Lake Saint Ann, Hungarian: Szent Anna-tó) is a crater lake located in the volcanic crater named "Puciosul" of the Eastern Carpathians, near Tuşnad in the Natural Reserve of Mohoş, Harghita County, Romania. It has an area of 0,22km² and has a maximum depth of 7 m.