rpm == 'rpm package manager'
deb == 'debian binary package format'

A deb is like an rpm, they are both binary files that have been pre-compiled for a specific computer architecture. The difference comes in the tools that manage the packages.

Debian's advantage here is that it supports a lot more architectures, has more packages, and resolves dependencies better in some cases than rpm.

Both systems are good although Debian's resolved dependencies first, rpm based systems had to wait until yum was developed before they had similar tools to apt-get.

Now rpm based systems have tools like zypper which are excellent. In some ways, rpms are easier to build for developers and debs are a little harder. But debs tend to be easier for users to install than rpms, though the difference is negligible.