Answer: when the speaker references something without giving much explanation/detail outside of the comparison itself. Helps writers/speakers simplify complex ideas/emotions/etc to the reader (if they actually understand the reference, that is)
Step-by-step explanation:
Saying someone is acting like someone you know personally or a person from a book or tv show; "She's such a Regina" referring to Regina George in the movie Mean Girls; "He acts like my dad"
Saying a place is like somewhere else; "Workplace is Hell", "Empty/abandoned place is like space"
(a complicated metaphor/simile)