What is the difference between uid and euid?

What is the difference between uid and euid? -- Linux general technology-Linux technology and application information. For details, refer to the following section. Uid is the user ID
Euid is a valid user ID
Can it be understood as follows:
Uid creates PROCESS p, while the access permission of p to files and resources is determined by euid (euid may be equal to uid or not equal to uid ).

Therefore:
1. If euid = 0, we can change the uid or the euid (root permission)
2. If euid! = 0, then the euid can be changed to uid or suid

Suid:
If it is a binary file and the set-uid bit is set, suid is the id of the file owner,
Otherwise, the suid is the uid of the current user.
This is my understanding, right? : 0wl; l1