Why is cyclopropane-1,1-diol stable The reason given me in my book is that it's stable due to steric relief.
The answer given on quora said "there is a lot of angle strain."

What exactly is steric relief ?

Can anyone help me elaborate how these points are contributing to the answer.Also what is the minimum angle to provide strain so that geminal diols are stable
The bonds in cyclopropane 1,1-diol are less strained than the cyclopropanone. 

The preferred/lowest energy for tetrahedral bond angles is 109.5 degrees so the closer they can get to that the lower the energy. In cyclopropanes the angles are 60.
The lowest energy angle for the R2C=O system (SP2) is 120 degrees, in cyclopropanone it is 60. This is a very strained and unstable system, anything that reduces that strain is a positive change energywise.

This problem is discussed here see problem 2