Question

what does the word cardboard denote in the poem? why has this word been used?​

Answer 1

The word cardboard donate’s the thick frame on which the photograph of poet’s mother and her cousins in the beach.
The word cardboard is used to refer to the past.The photograph was taken many years ago when the mother was alive.
In the present Photographs are not pasted on cardboards just as how the poets mother does not exist now.

Answer 2

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The word cardboard denotes the photograph pasted on a hard thick paper. This word

has been used to refer to a practice in the past when photographs were pasted on cardboard

and framed with glass front to preserve them.