Spf record dns

Hello,
What does this example mean?

v=spf1 include: spf protection outlook com ip4:157.55.9.128

I understood that it allows the whole Outlook domain to send emails to the mail server of another domain.
Why add an IP 157.55.9.128 in “ipv4”? It is not included in outlook com?
Thanks in advance

since enforcement not exist it meant +pass that specific ip will pass email authentication.

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