(i) Fixed Cost: It does not change with the change in the quantity of output. In other words, expenses on fixed factors remain unchanged irrespective of the level of output, whether the output is increased or decreased or even it becomes zero. For example, rent of the factory, watchman's wages, worker's salary. It is also called as 'Supplementary Cost' or 'Overhead Cost'.
(ii) Variable cost: These costs vary with the level of output. Examples of variable costs are: wages of temporary workers, cost of raw materials, fuel cost, etc., Variable cost is also called as Prime Cost, Special Cost, or Direct Cost.
(iii) Money cost: Production cost expressed in money terms is called as money cost. In other words, it is the total money expenses incurred by a firm in producing a commodity. Money cost includes the expenditures such as cost of raw materials, payment of wages and salaries, payment of rent, interest on capital, expenses on fuel and power, expenses on transportation and other types of production related costs. These costs are considered as out of pocket expenses. Money costs are also called as Prime Cost or Direct Cost or Accounting Cost or Explicit Cost.
(iv) Real cost: It refers to the payment made to compensate the efforts and sacrifices of all factor owners for their services in production. It includes the efforts and sacrifices of landlords in the use of land, capitalists to save and invest, and workers in foregoing leisure.
(v) Explicit Cost: Payment made to others for the purchase of factors of production is known as Explicit Costs. It refers to the actual expenditures of the firm to purchase or hire the inputs the firm needs. ego wages, payment of raw materials, rent, interest as capital. It is also called as Accounting Cost or Out of Pocket Cost or Money Cost.
(vi) Implicit Cost: Payment made to the use of resources that the firm already owns, is known as Implicit Cost. In simple terms, Implicit Cost refers to the imputed cost of a firm's self-owned and self-employed resources. A firm or producer may use his own land, building, machinery, car and other factors in the process of production. These costs are not recorded under normal accounting practices as no cash payments takes place. It is also called as Imputed Cost or Book Cost.

Short run Average Cost curves:
(i) Average Fixed Cost (AFC)
It refers to the fixed cost per unit of output. It is obtained by dividing the total fixed cost by the quantity of output. AFC = TFC / Q where, AFC denotes average fixed cost, TFC denotes total fixed cost and Q denotes quantity of output. For example, if TFC is 1000 and the quantity of output is 10, the AFC is Rs.100, obtained by dividing Rs.1000 by 10.
Table: Average Fixed Cost

It is to be noted that
(a) AFC declines as output increases, as fixed cost remains constant
(b) AFC curve is a downward sloping throughout its length, never touching X and Y axis. It is asymptotic to both the axes.
(c) The shape of the AFC curve is a rectangular hyperbola.
Average Variable Cost (AVC)
Table: Average Variable Cost

It refers to the total variable cost per unit of output. It is obtained by dividing total variable cost (TVC) by the quantity of output (Q). AVC = TVC / Q where, AVC denotes Average Variable cost, TVC denotes total variable cost and Q denotes quantity of output. For example, When the TVC is Rs. 300 and the quantity produced is 2, the AVC is f RS.150, (AVC = 300/2 = 150)
AVC is shown in table and Diagram
If TVC = Q³ - 18Q² + 9lQ
AVC = Q² -18Q + 91
It is to be noted that
(a) AVC declines initially and then increases with the increase of output.
(b) AVC declines up to a point and moves upwards steeply, due to the law of returns.
(c) AVC curve is a U-shaped curve.
Average Total Cost (ATC) or Average Cost (AC)
It refers to the total cost per unit of output. It can be obtained in two ways.
(1) By dividing the firm's total cost (TC) by the quantity of output (Q). ATC = TC / Q. For example, if TC is Rs. 1600 and quantity of output is Q = 4, the Average Total Cost is Rs. 400. (ATC = 1600/4 = 400)
If ATC is Q³ - 18Q² + 91Q +12, then AC = Q² - 18Q +91 + 12/Q
(2) By ATC is derived by adding together Average Fixed Cost (AFC) and Average Variable Cost (AVC) at each level of output ATC = AFC + AVC. For example, when Q = 2, TFC = 1000, TVC = 300; AFC = 500; AVC = 150; ATC = 650. ATC or AC is shown in table and Diagram

It should be noted that 
(a) ATC curve is also a 'U' shaped curve.
(b) Initially the ATC declines, reaches a minimum when the plant is operated optimally, and rises beyond the optimum output.
(c) The 'U' shape of the AC reflects the law of the variable proportions.

Total Revenue:
Total Revenue is the amount of income received by the firm from the sale of its product. It is obtained by multiplying the price of the commodity by the number of units sold.
Total Revenue - Constant Price

TR = P x Q
where,
TR denotes Total Revenue
P denotes Price and
Q denotes Quantity Sold.
When Price is Constant, the behaviour of TR is shown in above table and diagram assuming P = 5 when P = 5, TR = PQ.
When Price is declining with increase in quantity sold (E.g imperfect competition on the goods market) the behaviour of TR can be obtained from Demand function if Q = 11 - P
TR = P Q = 1 x 10 = 10
When P = 3, Q = 8 TR = 24
When P = 0, Q = 1 TR = 10
Total Revenue - Price declining

Fixed cost and variable cost: Fixed cost and variable cost are helpful in understanding the behaviour of costs over different levels of output.
Meaning of Fixed and Variable factors and costs:
Fixed and variable factors are with reference to short run production function. Short run is a period of time over which certain factors of production cannot be changed, and such factors are called fixed factors. The costs incurred on fixed factors are called fixed costs. The factors whose quantity can be changed in the short run are variable factors, and the costs incurred on variable factors are called variable costs
Fixed costs are those which are independent of output, that is, they do not change with changes in output. These costs are a 'fixed' amount, which must be incurred by a firm in the short run whether the output is small or large. E.g. contractual rent, interest on capital invested, salaries to the permanent staff, insurance premia and certain taxes. Variable costs are those costs, which are incurred on the employment of variable factors of production whose amount can be altered in the short run. Thus the total variable costs change with the level of output. It rises when output expands and falls when output contracts. When output is nil, variable cost becomes zero. These costs include payments such as wages of labour employed, prices of raw materials, fuel and power used arid the transport costs.

(i) Total revenue is the amount of income received by the firm from the sale of its products.
(ii) It is obtained by multiplying the price of the commodity by the number of units sold
(iii) TR = P x Q
Where TR = Total Revenue
P = Price
Q = Quantity Sold
For example: A cell phone company sold 100 Cell Phones with the price of Rs. 500 each TR is Rs. 50,000 (TR = 500 x 100 = 50,000)

When price is declining:
With increase in quantity sold the behaviour of TR is shown in the following table and diagram