Deltiology is the study and collection of postcards. Postcards (sometimes spelled out in two words as "post cards") became popular at the turn of the 20th Century, especially for sending short messages to friends and relatives. Professor Randall Rhoades of Ashland, Ohio, coined the word in 1945 that became the accepted description of the study of picture postcards. They were collected right from the start, and are still sought after today by collectors of pop culture, photography, advertising, wartime memorabilia, local history, and many other categories. Worldwide, deltiology is the third largest collecting hobby after stamp collecting and coin/banknote collecting.