noun
seasonal goods; seasonal items
Products sold only during a particular season, such as holiday decorations or seasonal foods.
この店はクリスマス前になると際物をたくさん並べる。
This shop puts out a lot of seasonal goods before Christmas.
The faddish products of that character sold out immediately.
noun
topical work; ephemeral writing
Novels, films, or plays that deal with recent events or current trends, often of passing interest.
彼の新作は昨年の事件を題材にした際物だ。
His new work is a topical piece based on last year's incident.
流行り物 is a broader term for anything fashionable or in vogue, while 際物 emphasizes the opportunistic or short-lived nature of the product.
Compound of 際 (kiwa, 'edge, verge, occasion') and 物 (mono, 'thing'). The exact derivation is uncertain, but it likely refers to goods tied to a specific time or occasion.