What is the difference between the Default Tax Label and the Name on each tax rate?

Both are names customers can see, used in different places:

• Name on a rate (for example CGST or VAT) is the label on that rate's own line at checkout and on the order. New rates start with "Tax", so change it.
• Default Tax Label (in Tax Settings) is used when a rate has no name. When several rates apply to one order, it is also the single combined tax name saved on the order. Invoice templates print that name.

Set both on Settings → Store Settings → Manage Tax. Click Tax Settings, enter the Default Tax Label (for example GST) and click Save Settings. Then give each rate a clear Name.