A genetically modified organism (GMO) is an organism whose genetic material has been altered using genetic engineering techniques. Organisms that have been genetically modified include micro-organisms such as bacteria and yeast, plants, fish, and mammals. GMOs are the source of genetically modified foods, and are also widely used in scientific research and to produce useful goods other than food.
It depends on where you live. I’m in the U.S. so it’s not a law that we have to be told if something is a GMO product =\
But a lot of vegan brands like Silk specifically label on their products that it does not contain any GMOs because that’s something to be proud of.