This is a portmanteau word that combines oshare (fashionable) and picnic.
It refers to the phenomenon of people uploading attractive photos to social media by carefully staging everything from the food to the picnic blanket.
Since a popular model introduced this some years ago on her blog, it has become quite the thing.
wo awaseta kotoba
(a) portmanteau word that combines
(the) picnic blanket
shashinn bae suru
carefully staging (everything)
(it) refers to (the phenomenon of people)
suunenn mae ni
some years ago
ninnki moderu ga
(a) popular model
(quite) the thing
(it) has become