A very powerful weed
killer from the Scotts
company. It comes in varing sizes of sprays from small bottles to very large "bush-clearing" jugs. They also produce a foam Roundup so that you can see where you have and haven't sprayed. The active ingredient is glyphosate
Roundup commercials have traditionally been fairly memorable - weeds that talk about a spray that killed their friends, etc.
Roundup is also the name of an open source software project. It is a very flexible bug and issue tracker written in the python programming language.