What is a for loop doing in a list / dictionary / set (question looking for comprehension syntax)

• name-that-syntax
• list-comprehension
• dict-comprehension

The terminology makes finding a canonical “That’s a list / dict / etc. comprehension” question hard.

• Why is there a loop in this dictionary?
• Python for-in loop preceded by a variable
• What does "list comprehension" and similar mean? How does it work and how can I use it?