What the meaning of two commit ID in a merge commit's log

[wuzhouhui <wuzhouhui14@xxxxxxxxxxxxxxxx>]

Hi,

When I use "git log" to display commit log, I see there are
two commit IDs in a merge commit, e.g.

    commit 2187f215ebaac73ddbd814696d7c7fa34f0c3de0
    Merge: 2d3145f8d280 fbd542971aa1
    Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
    Date:   Tue Dec 17 13:27:02 2019 -0800

        Merge tag 'for-5.5-rc2-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux

In the previous example, we can see two commit IDs: 2d3145f8d280 and
fbd542971aa1. So, what's the meaning of them, precisely.

Thanks