There is no definition of an inode in the POSIX standard.
The POSIX Programmers Guide
by Donald Lewine says POSIX uses the term “file serial number” to refer to what’s commonly known as an i-node number, namely the unique number of a file entry in a filesystem.
ino_t shall be defined as unsigned integer types.
Interestingly, the standard does include the word “inode”, as @apricot boy mentions, but I also can’t find a definition of the term.
Perhaps the closest is:
ino_t st_ino File serial number.
In this comment, Johan Myréen says Wikipedia is probably confusing an inode with the contents of the
stat structure does contain device information and the other information Wikipedia erroneously says is included in the inode.