O/ρ is a reference to two quantities in IT performance engineering:

• Big-O notation is used to describe time complexity of algorithms - how algorithm execution time scales with the volume of the input.
• $\rho$ is defined to be the utilization of queuing systems.

Inadequate or lack of attention for scalability and utilization is a common cause for failing IT projects. Scalability matters - perhaps the mother of all functionality, as something that does not respond or cannot complete in time, really has no functionality at all.

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