average cost

mean expense of a product or manufacturing factor

In economics, average cost is equal to total cost divided by the number of goods produced (Quantity-Q). It is also equal to the sum of average variable costs (total variable costs divided by Q) plus average fixed costs (total fixed costs divided by Q). Average costs may be dependent on the time period considered (increasing production may be expensive or impossible in the short term, for example). Average costs affect the supply curve and are a fundamental component of supply and demand.
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Under the average-cost method, it is assumed that the cost of inventory is based on the average cost of the goods available for sale during the period. Average cost is computed by dividing the total cost of goods available for sale by the total units available for sale. This gives a weighted-average unit cost that is applied to the units in the ending inventory.
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Noun
1. total cost for all units bought (or produced) divided by the number of units
(hypernym) monetary value, price, cost

In the context of investing, refers to the average cost of shares or stock  bought at different prices over time.

the average cost per unit of production of a set or group of products; the total cost of production divided by the total number produced; the Unit Cost. See Long-Run Average Cost; Short-Run Average Cost.