To do business people do activities. Activities have defined (at times surprises!) real, financial flows and objectives. Every Activity is also associated with information/data inputs and outputs.
A set of activities with common objective may be grouped as a process. Every business has Processes which can be grouped into broad functional areas, for example, Sales, Service, Logistics, Accounting etc. The boundaries do not clearly separate as many processes overlap into functional other than to which they belong. This functional grouping (or domains) have processes embedded in them.
Businesses which do similar value addition are grouped functionally or on some other perspective. Businesses grouped together share similar (if not congruent) processes and groupings thereof.
At the same time there are certain Domains which share very similar Processes across Business Groupings. An example would be accounts. Even though no two businesses are the same, there are some Domains/Processes which are quite common (if not exactly same) to most of the Businesses.
If not developed in present times, most processes have been developed in an era when there was no IT.
Not all processes are Optimal - a perfect mix of ideal and practical.