WHAT IS IT?  Books, containing all of the regulations, hundreds and hundreds of them, in standardized format, published by the GPO (US Government Printing Office), available online. 

Regulations are not laws. 

Laws - are made by elected officials (for Federal laws, the US Congress).  

Regulations are made by regulators (government employees).  Laws give agencies such as OSHA, EPA, DOT, NRC.... the power to make and enforce regulations.