Clamp 0 Scalar will restrict any values below 0 leaving them at zero. Anything above 0 remains the same.
Using a cosine signal with peaks having a value range of -2 to 2 to displace a surface...
Clamp_0_Scalar_01.jpg
...Clamp 0 Scalar cuts off values below 0 and leave them at 0
Clamp_0_Scalar_02.jpg
This node is useful in removing negative values when combining multiple sources to leave a desired range of 0 and beyond.
If there's any errors, omissions or questions about the above, please leave a comment and we will add further details in this post when relevant.
https://planetside.co.uk/wiki/index.php?title=Clamp_0_Scalar