How to understand Git's Fast Forward and no fast foward merge mode?

I have read a lot of materials on the Internet, many of which are translated into foreign languages, but I am still confused after reading them.

can I understand that Fast Forward merges the development branch directly into the master branch without keeping the commit record on the development branch. In other words, when others are reading the commit history of the master branch, they can only see that the development branch has a record of merging into master, but can"t see the specific commit, of the development branch before it is merged into master, right?

Git
Mar.05,2021

look at the picture

you can only see that the development branch has been merged into master, but you cannot see what commit the development branch has before merging into master

if you execute Fast Forward, the developer will not see this branch at all, just like commit directly in master.

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MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1eaaae2-47db7.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1eaaae2-47db7.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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