Help: What's the raw packet socket?

Dear all,

I am a primary programmer on network.
From some documents, I have read that some interfaces between host and
clients are programed by the raw packet socket. My question is:

1. What's the raw packet socket?
2. What's the differnce between a general socket and the raw packet
socket?
3. Where could I found more details about the raw packet socket?

Thanks

Jian Zhang

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