Typically a website address starts with www. – sometimes they dont.
But if you pay attention, you will see some websites using other variations such as www1 or www2.
Why do they do this?
The first thing to know is there’s no need to be concerned – it doesn’t doesn’t mean the website has been “hacked” or they’re using a “newer” version of the internet.
Here are the four main reasons I’ve seen this …
Reason 1: Because they can !
The www. part of a website address is known as the “sub-domain” – there’s no standard to say it has to be used or be www. – that’s just a common practice that came from the early days of the Internet. So it’s possible a website has chosen to just be different.
Reason 2: Separate systems

Reason 3: Static “cookie-less” domain

Reason 4: Load balance traffic

Does it matter?
No – not at all.
If the website’s domains and security certificates (SSL/HTTPS) have been setup correctly it won’t make any difference to the users.
It may very slightly speed up the load speed of a website – but in practice it’s barely noticeable.
It generally comes down to how a website’s infrastructure is managed.