From the Good Doctor's favorite dictionary:
e·phem·er·a ( ĭ-fĕm
'-ər-ə)
NOUN:
A plural of
ephemeron.
e·phem·er·on ( ĭ-fĕm
' ə-rŏn' )
NOUN:pl. e·phem·er·a (-ər-ə) or
e·phem·er·ons 1. A short-lived thing.
2.
ephemera Printed matter of passing interest.
ETYMOLOGY:Greek
ephēmeron,
mayfly, from neuter of
ephmeros,
daily, short-lived ; see
ephemeral
People collect ephemera (I've never seen the singular in use before just now), which includes things like newspaper articles (clippings), train schedules, postcards, political campaign buttons and bumper stickers -- anything that is meant for a passing usage but which at some later date may give some insight into time and place it was first used.
In the case you cited, it's not the trial that's ephemeral but the items mentioned: newspaper clippings, photographs, booklets, and so forth ARE the ephemera; the official court records would not be. Other categories of ephemera are letters, posters, postcards, menus, and just about anything that wasn't printed with the intention of it being kept. Go to E-Bay and search for Ephemera to see the types of things that fit this category. I suppose that the prayer cards one picks up at a funeral would also qualify.
I drove my mother to a humongous flea market in Kutztown, PA, many years ago to visit some friends (former neighbors) who had a booth their. They carried some ephemera which included items sent to listeners of the old "Lum and Abner" radio show. Another example would be the bill of sale for a sewing machine sold back in the 1930s, or a hospital bill from long ago.