Well, I don't know, Mr. AC. To which "people" do you refer? Most "people" I know in astronomy define an "aperture" in the same way Wikipedia does [wikipedia.org]:
[T]he aperture stop is the stop that determines the ray cone angle, or equivalently the brightness, at an image point.
In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself. For example, in a telescope the aperture stop is typically the edges of the objective lens or mirror (or of the mount that holds it). One then speaks of a telescope as having, for example, a 100 centimeter aperture. [emphasis added]
Most astronomers I know actually would, in fact, tell you that aperture masking turns a 10m aperture into a cm-range aperture, since the sensitivity of the resulting telescope would be that of one having a much smaller diameter. That's how most cameras work . . . f-stops, anyone?
Strictly speaking, the usual use of the word "aperture" in astronomy actually means
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