What is the written-out word for O_EXCL

I was writing a safe enum class for the different file flags listed in open(3), when I noticed, that I couldn't find the written-out word for O_EXCL.

enum class Flags {
    readOnly, // O_RDONLY
    truncate, // O_TRUNC
    ?         // O_EXCL
};

Two possible meanings come into my mind:

• OPEN_EXCLUSIVE
• OPEN_EXISTS_CLOSE

But I can't find any resources on the intended meaning.