The upward-sloping portion of the perfectly competitive firm's average total cost curve is the firm's short-run supply curve.

Average Total Cost Curve

A graph that shows a firm's per-unit cost (both fixed and variable) at various levels of output.

Upward-sloping

Describes a curve on a graph that moves higher as it goes from left to right, often used to illustrate the relationship between price and supplied quantity in supply curves.

Short-run Supply Curve

A graphical representation showing the quantity of goods that producers are willing to supply at various prices over a short period, where at least one input is fixed.