Substrate?

Hey all I am growing a Dinafem Roadrunner it says it needs 20 hrs of sunlight no problem there outside in VT but also substrate about 4 liters what is this. Any help would be much appreciated. Did a search here and found a few threads but it was all jibberish to me!

That's just the material you grow in: soil, coco, rockwool, etc. It's a nice little word for whatever medium you use.

Cheers and good luck!

thank you!