Step 1: Formula.
\[
\text{Operating Ratio} = \frac{\text{Operating Cost}}{\text{Net Sales}} \times 100
\]
Step 2: Nature.
Operating ratio shows the percentage of sales consumed by operating expenses. Lower ratio = higher profitability.
Step 3: Classification.
Since it measures efficiency of operations and profitability, it belongs to the category of Profitability Ratios.
Step 4: Conclude.
Hence, Operating ratio is a profitability ratio.
Final Answer:
\[
\boxed{\text{Profitability ratio}}
\]