Since we now know that we can create thousands of VLANs and they can span across multiple switches, these could get confusing even for the switches. You must remember that by default, regular access ports remove any VLAN ID information. Hence, we trunk ports between switches and switches to routers, so ports can look at the frame and be able to identify or tag that port with a VLAN ID.
The other great thing about trunk ports is that they permit tagged or untagged VLANs to go through their ports.
Any VLAN that is Not Tagged, Native, or Default belongs to access ports and they already have a Port VLAN Identifier within the frame, so they could go across trunk ports or access ports.