.gitignore
is a text file comprising a list of files in your directory that git will ignore or not add/update in the repository.
.gitkeep
Since Git removes or doesn't add empty directories to a repository, .gitkeep is sort of a hack (I don't think it's officially named as a part of Git) to keep empty directories in the repository.
Just do a touch /path/to/emptydirectory/.gitkeep
to add the file, and Git will now be able to maintain this directory in the repository.