Q.Define Cost. How is it different from an ordinary expense figure?

In everyday language "cost" and "expense" are often used interchangeably, but in cost accounting, cost is always tied to a specific object.

Cost is the monetary measurement of the resources — materials, labour and expenses — that are sacrificed or used up to produce a specific product, complete a specific job, or render a specific service. Unlike a general expense figure (say, total factory rent for the month), a cost figure is always related to a defined cost object: the cost of one unit of a product, the cost of completing one job, the cost of running one process. This is what allows costs to be compared, controlled and used for pricing decisions, since a cost figure with no object attached to it cannot be meaningfully analysed.

Cost is one of the three foundational terms of this subject and needs to be defined precisely, since the whole subject builds on it.

Cost is the monetary measurement of the resources — materials consumed, labour employed, and other expenses incurred — that are sacrificed or used up in order to produce a specific product, complete a specific job, or render a specific service. Three points follow directly from this definition:

1. It is always expressed in money terms. Even though the underlying resources (hours of labour, kilograms of material) are physical quantities, cost translates them into a single monetary figure so that unlike things (labour hours, material weight, machine time) can be added together meaningfully.
2. It is always attached to a specific object. A cost figure only makes sense when it answers "the cost of what?" — the cost of one unit of output, the cost of one job, the cost of running one process for a month. A bare total expenditure figure with no object attached is not, by itself, a "cost" in the technical sense used in this subject.
3. It is historical or planned, but always specific. Whether we are talking about cost already incurred (historical cost) or cost expected to be incurred (estimated/standard cost), the figure is always tied to a defined product, job, or service — never a vague aggregate.

This is exactly what separates "cost" from an everyday "expense" figure such as "this month's total factory expenses were ₹5,00,000" — that total, on its own, does not tell us the cost of any particular product or job until it is analysed and related to specific cost objects, which is precisely the work that Costing and Cost Accounting are set up to do.

Students often write "cost is the amount of money spent by a business" and stop there — this misses the crucial requirement that cost must be related to a specific object (a product/job/service). A vague, un-related total expenditure figure is not, technically, a "cost" in this subject's sense; always name the object the cost relates to in your answer.