What is planck curvature?

[kini.Amith]

I was reading a paper by Starobinsky on spectrum of relict gravitational radiation. He uses the term Planck curvature as follows
"We construct a model in which the universe was perpetually in the quantum state with the radius of curvature of the order of Planck curvature, and later left this state to enter the classical expansion stage."
What does this term mean?

 

[PAllen]

Often a wooden board will curve as it ages, if it hasn't been dried properly. This is known as plank curvature. Alternatively, ancient ship builders dried planks under stress to build hulls, resulting in plank curvature. The relativistic generalization of this adds a c.

Real answer: The following is the very first google hit for "Planck curvature". Good form asking a question here is to show some sign of having spent more than 5 seconds trying to find the answer, and framing your question in relation to the result of such effort.

https://books.google.com/books?id=HEHwCAAAQBAJ&pg=PA348&lpg=PA348&dq="planck+curvature"&source=bl&ots=nzzbLEK-b9&sig=XDKbUifB-sCbf7AKwlfEeczpXHc&hl=en&sa=X&ved=0ahUKEwikrOy0_8bMAhVJFx4KHRIiDhwQ6AEIHDAA#v=onepage&q="planck curvature"&f=false