A Cinematic Universe is the whole Filmography for a certain brand, company etc.
The
DreamWorks universe for example,
The most popular DreamWorks movies are Shrek,
Puss in Boots, Kung-Fu Panda, Madagascar etc.
The Shrek part of the DreamWorks Cinematic Universe would contain all Shrek movies, the full character list (background characters included), and the timeline.
The same would go for the other movies. Timeline is less important for one specific movie (we don't need to have everything written down, some things that happen won't be important to the story at all, and aren't important to the timeline), but the order of the movies is more important. The example down below shows the difference.
Example:
Shrek is a disgusting
swamp monster, he has a
simple life and is a simple swamp monster .. (the other parts of the movie written out.) ❌
(Too much information, practically a spoiler.)
Shrek is a swamp monster who saves, falls in love with, and marries a princess with a Donkey by his side. ✅
(Short, literal summary of the first Shrek movie.)
An example how it would be used in a conversation is down below. (DreamWorks themed.)