expression, noun
Often refers to a young woman, but can be used for young people in general. Casual and somewhat colloquial.
あの若い子は誰？
Who is that young person?
最近の若い子はSNSをよく使う。
Young people these days use social media a lot.
若者 is a more standard and neutral term for 'young people', while 若い子 is more casual and often implies a younger, perhaps teenage or early twenties, person.
Phrase composed of 若い (young) and 子 (child/person).