A git rebase is like a git merge done through rose-coloured glasses.

You can see it for yourself by doing this little experiment. Assuming the alice directory is a valid git repository:

$ cd alice
$ echo "foo" >> rebase.episode
$ git add rebase.episode ; git commit -m 'begin rebase episode'
$ git checkout -b monsters

$ git branch
* monsters
master
$ echo "ghoul" >> ghoul.txt
$ git add ghoul.txt ; git commit -m 'ghoul'
$ git checkout master
$ echo "rogue" >> rogue.txt
$ git add rogue.txt ; git commit -m 'rogue'

$ git checkout monsters
$ echo "dragon" >> dragon.txt
$ git add dragon.txt ; git commit -m 'dragon'

$ git checkout master
$ echo "paladin" >> paladin.txt
$ git add paladin.txt ; git commit -m 'paladin'

You have now emulated a bunch of activity on two separate branches of a git repository. Create a copy of the repo so that you can perform two separate git actions.

$ cd ..
$ cp -r alice alice-merge
$ cp -r alice alice-base

Do an honest merge:

$ cd alice-merge
$ git checkout master
$ git merge monsters

The log shows you an accurate representation what got merged, and how all those changes came to be:

$ git log --oneline
123456 Merged monsters into master
789101 paladin
112131 dragon
415161 rogue
718191 ghoul
7ef217 begin rebase episode

Now perform a rebase.

$ cd ../alice-base
$ git checkout master
$ git rebase monsters

The log displays a different story than what really happened.

123456 Merged monsters into master
8e9122 paladin
21d163 rogue
912a3f dragon
51c098 ghoul
7ef217 begin rebase episode

Better? Worse? YOU DECIDE!