thumb|A historical example of ephemera
Ephemera () are items which were not originally designed to be retained or preserved, but have been collected or retained. The word is both plural and singular.
One definition for ephemera is "the minor transient documents of everyday life". Ephemera are often paper-based, printed items, including menus, ticket stubs, newspapers, postcards, posters, sheet music, stickers, and greeting cards. However, since the 1990s, the term has been used to refer to digital artefacts or texts. The initial sense extended to the mayfly and other short-lived insects and flowers, belonging to the biological order Ephemeroptera.
In 1751, Samuel Johnson used the term ephemerae in reference to "the papers of the day". Ephemeral, by the mid-19th century, began to be used to generically refer to printed items. The degree to which ephemera is ephemeral is due in part to the value bestowed upon it. Over time, the ephemerality of certain ephemera may change, as items fall in and out of fashion or popularity with collectors.
As a conceptual category, ephemera has interested scholars. Henry Jenkins has argued that the emergence of ephemera, and the interest that some people show in collecting items that other people throw away, showcases the immaterial nature of culture arising in daily life. Rick Prelinger noted that when a piece of ephemera is preserved, and greater value is placed upon it, the object then arguably stops being ephemera.
Categorising types of ephemera has presented difficulties to fixed systems in library science and historiography due to the ambiguity of the kinds of items that might be included. Challenges pertaining to ephemera include determining its creator, purpose, date and location of origin and impact thereof. Determining its worth in a present context, distinct from its perhaps obscured purpose, is also of interest.
The breadth of printed ephemera is vast and varied, often eluding simple definition. Librarians often conflate ephemera with grey literature whereas collectors often broaden the scope and definition of ephemera. José Esteban Muñoz considered the characteristics of ephemera to be subversion and social experience; Alison Byerly described ephemera as the response to cultural trends. Wasserman, who defined ephemera as "objects destined for disappearance or destruction", categorised the following as ephemera:
Further items that have been categorised as ephemera include: posters, album covers, meeting minutes, buttons, stickers, financial records and personal memorabilia; announcements of events in a life, such as a birth, a death, a graduation or marriage, have been described as ephemera. Textual material, uniformly, could be considered ephemera. Historically, there has been various categories of ephemera. Genres may be defined by function or encompass and detail a specific item.