How is general liability insurance different from public liability insurance?

General liability covers Public and Producs Liability, therefore by having General Liability cover, public liability is covered also.

There is no difference.

There is no such thing as a "comprehensive" general liability policy. It is "commercial" to differentiate it from personal-lines coverage. It is commercial general liability policy, or CGL; a...

Usually this is insurance taken out by a business to protect against the risk of being sued - or held liable - for damage or injury that occur while they're conducting their business

General Liability insurance is purchased through any insurer that provides commercial insurance lines coverage.