The phrase "several gigabytes" means a large amount of digital information, like files or data, that can be stored or transferred. It is around a few billion bytes, which is a unit used to measure computer storage capacity. Full definition
Elements such as texture quality and shadow resolution in particular really need GPUs with several gigabytes of RAM when maxed out in order to provide a playable experience. (eurogamer.net)
Hell, even if you buy the physical disc you'll end up with several gigabytes of data usage just for updates. (howtogeek.com)
Some devices now store several gigabytes of data — enough to stash hundreds of large photos, or even several thousand. (edutopia.org)