fiber. The way fiber works is it goes from the fiber to a device that converts it to Ethernet, this is called an ONT.
Then the Ethernet needs a modem/router usually a gateway device.
These days a lot of those are combined into one, so fiber comes in to the one device and then you get Ethernet.
Rarely the ONT will be outside of your unit, say like in an apartment, and all you see is an Ethernet cable.
You can replace your gateway entirely with a smart SFC module, if you have access to the actual optical fiber cable.
Otherwise ten gig PCIe cards are really cheap on eBay, or just fs.com ten gig RJ45 SFC module.
Also there are thunderbolt SFC devices to get ten gig to a laptop.
Personally my LAN uses one hundred gigabit because the cards are like $70 each.