Positive pressure is a pressure within a system that is greater than the environment that surrounds that system.
There are multiple meanings of "system".
What does "system" mean in the given context?
I am sure they are using "system" in a technical scientific sense. However, you could say that the system is any closed environment. ") Does this help?
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I am sure they are using "system" in a technical scientific sense. However, you could say that the system is any closed environment.
"When the air pressure in the laboratory is greater than the air pressure outside, we say that the lab has positive air pressure." (In this example, "the lab" is "the system.")
Does this help?