A word or phrase popular and widely used temporarily
When to use
temporary trendy word, popular among masses, usage of trendy words
The nuance
유행어 are words or expressions popular among many people for a limited time; they may fade away later.
유행어 (yu-haeng-eo, yuhaengeo) · 신조어 (sin-jo-eo, sinjoeo) · 줄임말 (jul-im-mal, julimmal)
유행어 (yuhaeng-eo) are trendy words, 신조어 (sinjoe) are newly coined words, and 줄임말 (julimmal) are abbreviations of longer words.

One lane per word — no nested boxes, just the gist.
A word or phrase popular and widely used temporarily
When to use
temporary trendy word, popular among masses, usage of trendy words
The nuance
유행어 are words or expressions popular among many people for a limited time; they may fade away later.
Newly created word or expression recently coined
When to use
recently coined word, new meaning assigned, creation of new words
The nuance
신조어 refers to newly created words or expressions that did not exist before; they may become trendy words but not necessarily.
An expression made by shortening a long word or phrase
When to use
abbreviation of long words, simplification in daily speech, form of shortened words
The nuance
줄임말 are words formed by shortening longer words or phrases; unlike 신조어 or 유행어, they often modify existing words.
요즘 '인싸'는 인기 있는 유행어예요.
yo-jeum 'in-ssa'neun in-gi iss-neun yu-haeng-eo-ye-yo., yo jeum 'in ssa'neun in gi iss neun yu haeng eo ye yo.
'인싸' was popular temporarily, fitting the 유행어 category.
'인싸'는 신조어가 아니에요.
'in-ssa'neun sin-jo-eo-ga a-ni-e-yo., 'in ssa'neun sin jo eo ga a ni e yo.
'인싸' is not a 신조어 but a 유행어 used for several years; 신조어 must be newly created.
'셀카'는 줄임말이에요.
'sel-ka'neun jul-im-mal-i-e-yo., 'sel ka'neun jul im mal i e yo.
'셀카' is a 줄임말 shortened from '셀프 카메라'.
'셀카'는 신조어가 아니에요.
'sel-ka'neun sin-jo-eo-ga a-ni-e-yo., 'sel ka'neun sin jo eo ga a ni e yo.
'셀카' is not newly coined but a shortened form.
'엄친아'는 신조어예요.
'eom-chin-a'neun sin-jo-eo-ye-yo., 'eom chin a'neun sin jo eo ye yo.
'엄친아' is a recently created new word, qualifying as 신조어.
'엄친아'는 줄임말이에요.
'eom-chin-a'neun jul-im-mal-i-e-yo., 'eom chin a'neun jul im mal i e yo.
'엄친아' is not an abbreviation but a new word; 줄임말 must shorten longer words.
'갑분싸'는 줄임말이면서 유행어예요.
'gap-bun-ssa'neun jul-im-mal-i-myeon-seo yu-haeng-eo-ye-yo., 'gap bun ssa'neun jul im mal i myeon seo yu haeng eo ye yo.
'갑분싸' shortens a phrase (줄임말) and is also a trendy word (유행어).
'갑분싸'는 신조어가 아니에요.
'gap-bun-ssa'neun sin-jo-eo-ga a-ni-e-yo., 'gap bun ssa'neun sin jo eo ga a ni e yo.
'갑분싸' is primarily an abbreviation and trendy word, not a newly coined standalone word.
What type of word is '셀카'?
What kind of word is '엄친아'?
What kind of word is '갑분싸'?
What kind of word is '인싸'?