1. Things that exist or are used or enjoyed for only a short time, something of no lasting significance
2. paper items (such as posters, broadsides, and tickets) that were originally meant to be discarded after use but have since become collectibles
3. an ephemerid (insect of the order Ephemeroptera, comprising the mayflies)
Here, six writers remind us of the ephemera many of us will miss when smartphones inevitably make wallets obsolete—and a few of the worthy trade-offs our devices bring. (Will the Smartphone Ever Truly Replace Your Beloved Wallet? Wall Street Journal)
Events are the ephemera of history; they pass across its stage like fireflies, hardly glimpsed before they settle back into darkness and as often as not into oblivion. (Fernand Braudel, The Mediterranean)
The Ephemera is the fly which is born but to die, living a single hour of love. (Jules Michelet, The Insect)
Late 16th century: plural of ephemeron, from Greek, neuter of ephemeros 'lasting only a day'. As a singular noun the word originally denoted a plant said by ancient writers to last only one day, or an insect with a short lifespan, and hence was applied (late 18th century) to a person or thing of short-lived interest. Current use has been influenced by plurals such as trivia and memorabilia. (Oxford Dictionaries)
Originally a medical term, from Medieval Latin ephemera (febris) '(fever) lasting a day,' from fem. of ephemerus, from Greek ephemeros 'daily, for the day,' also 'lasting or living only one day, short-lived,' from epi 'on' + hemerai, dative of hemera 'day,' from PIE *Hehmer 'day.' Sense extended 17c. to short-lived insects (Modern Latin ephemera musca) and flowers; general sense of 'thing of transitory existence' is first attested 1751. Compare Greek ephemeroi 'men,' literally 'creatures of a day.' (Online Etymological Dictionary).