What is 'class' in HTML?

“class” is part of HTML and it does not affect the tag.
So yes,

<h1 class="arbitrary-name"> arbitrary title </h1>

Is the same as:

<h1> arbitrary title </h1>

https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/class

thanks Andrew,
so which one is ‘better’ ?

sorry for the newbie question.

You’ll need to expand on your question because it doesn’t make sense.