What does it mean for the universe to be globally flat, What does it mean for the universe to be globally flat, spherical or hyperbolic? How does it relate to whether the universe will recollapse, or never stop expanding, or expand at an accelerating rate? How does it relate to local geometry, eg. the ratio of a lab-measurable circle's circumference to diameter? Is this the same as positive vs. negative intrinsic curvature? How does it relate to the "average energy density" (I understand +ve cosmological constant is equivalent to a uniform distribution of "dark energy", or "material" with negative mass)? How about the total mass in the universe?