Newer downloads of the Raspberry Pi Raspbian image come with something called mathematica and wolfram, the latter is a language to a the mathematica maths program.
This takes up nearly 500mb of diskspace. If you don’t require this software you can remove it with
sudo apt-get remove wolfram-engine
You may need to delete the icons manually, if there are still links on the desktop.
I would assume to put this back you simply reinstall it with
sudo apt-get install wolfram-engine