What does this mean(Radians) in bevel
?
Apply the bevel at the set angle.
For more information, go to the manual. 
https://docs.blender.org/manual/en/latest/modeling/modifiers/generate/bevel.html
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It means that only edges with an angle between its faces, above a certain number will be beveled.
In your example, 0.523599 radians is equal to 30º, so bevel will only affect the edges that connect faces with an angle bigger than 30 degrees.
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Radians …are another way to measure angles (mostly used in mathematics).
You may have to elaborate this to get a more suited answer.
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