In Ubuntu and Linux in general, some packages include several binary files. A clear example of that behavior is the package libav-tools which installs a group of executables such as avconv, avplay ...

Let's explore this example. If, for some reason, you want to uninstall avconv, you need to find which package the previous command is contained in. To find the package responsible for the installation of avconv, simply run the following command in a terminal:

sudo dpkg -S $(which avconv)

The aforementioned command will output the following line:

libav-tools: /usr/bin/avplay

As you can see in the example above, avconv belongs to libav-tools so to uninstall it, issue the following command into a terminal window:

sudo apt-get remove libav-tools