A class is an important concept in TAD. Those familiar with object oriented languages will understand it immediately. But an architect often may not know this

A class is simply an abstract container. Why abstract? Because there is no Physical container It is only in our mind. Like a grouping. A class is used to gather together (not physically, but in your mind) a set of objects that logically all share the same or similar properties.

In the real world; the class of humans would be you, your spouse, children etc. Of course the term human is a name given to an abstract collection. For e.g. you will not see one special area in the world or a space where all humans would be cornered together! Similarly, a class is just a name you give to the collection

A class can have sub-classes too. For example; under the class called humans we have broadly two other sub-classes called males and females Now we know that both of them do belong to the class called humans but there are indeed some properties of males that are not seen in females and vice-versa