The scientific name for weed is not a single term, as the word "weed" is a general term referring to any unwanted plant growing in a particular place.

However, if you are referring to the marijuana plant, its scientific name is Cannabis sativa.

If you're interested in the scientific name of a specific weed, you'll need to tell me what type of weed you are interested in. For example:

* Dandelion: *Taraxacum officinale*

* Crabgrass: *Digitaria sanguinalis*

* Poison ivy: *Toxicodendron radicans*

Let me know what weed you're looking for, and I can help you find its scientific name.