Meaning:
“小” means “small,” and “作文” refers to “essays written by students as assigned by teachers.” Literally the term refers to a short essay written by a student. However, Chinese netizens have come up with a creative use for this term and use it to refer to long posts on social media or long paragraphs posted during online chats, which give the impression that someone has written a short essay. Usually the language is good and the contents are thoughtful if a post is described as “a short essay.”
Example:
A: 小李昨天在朋友圈发的关于居家隔离的小作文你看了吗？
Xiǎolǐ zuótiān zài péngyǒuquān fā de guānyú jūjiā gélí de xiǎozuòwén nǐ kàn le ma？
Did you see the long post Xiao Li left on his WeChat Moments yesterday, the one about his quarantine at home?
B: 看了，真没想到他对生活点滴的体会还挺深刻的。
Kàn le，zhēn méi xiǎngdào tā duì shēnghuó diǎndī de tǐhuì hái tǐng shēnkè de。
I did. I didn’t know he had such profound thoughts about the details of daily life.