What actually is a loss

Loss is a reduction in economic resources. The second question correlates to opportunity cost 

is opportunity cost also a loss ? by giving up are we loosing potential income

An opportunity cost is not an expense and so it is not a loss. In full cost plus pricing, these opportunity costs foregone will be added to the price of the product

opportunity cost as the word signifies is possible revenue foregone.

No stanza in revenue recognition mentions about future revenues without an economic transaction. It is technically a cost which will not reduce revenues cause they are capitalised and opportunity costs are huge. Hence they are avoided and when necessary allocated to the product cost.

Yes Kev Men relevant costing and decision making based on Full Cost Plus Pricing (with or without an opportunity cost, what will be the selling price). I did not learn these in things in MBA as the curriculum doesn't have anything apart from definitions and formulas. Some good management lies in my MSc curriculum as its specialized in international accounts and finance. In fact, my old lecturer told around the world people can pass MBA because its all a GIST and not consummate in every module. He also advised everyone in the class that they have to enhance their education through specialization because an MBA is valid only for 2-3 years. It will expire after that and that people must work, save money and join a new course. Which I did.

another example attached below

Hence I urge all of future graduates to -'Choose a great curriculum to study and not a great college'. I am also passed graduate like millions but I have complete leverage due to my curriculum and not notes or lecturers or colleges. Thats freedom