Interweb is a name often used humorously by more experienced users of the Internet to refer to the World Wide Web or the Internet. The word is generally used as a connotation of newbieness or used in context of inexperienced usage of the Internet. For example:

"I'm going to go over to my grandmother's house and explain the Interweb to her. She is still having trouble sending emails."

It's also used in oversimplifications of the complex system that is the Internet. Often times, experienced users and technicians will become jaded with all the technology's complexities and prefer to use simple terms in an explanation. This often is proceeded by an hour or more of dealing with users who feel they must know everything about the workings of computers, yet don't actively take part in their own learning. For example:

tech: "I've installed a new email client that should be better about dealing with attachments. You should be safe from email viruses, as long as you don't click on the EXE's in your emails."

user: "Wonderful. I'm curious, how did the viruses get there in the first place?"

tech: "Well, they're written by malicious coders who like to exploit known vulnerabilities in a piece of software, in your case - Outlook. Generally they're there to prove a weakness of a piece of software or to make the writer look 'cool' to the writer's peers."

user: "Ah. How did they get onto my computer then?"

tech: "Someone sent one to you through an email."

user: "I see. What can I do to stop people from sending them to my email?"

tech: "Well, you can't. That's what I just fixed - you are now using an email client that doesn't automatically run the viruses when they're received."

user: "I see. So, people can't send me viruses anymore?"

tech: "*grumble* No. Through the magic of the Interweb, you'll still get viruses. Your computer will just ignore them, as long as you don't click on them."

user: "But what if my friend sends them to me? Can I click on those?"

tech: ...

Note: To protect the innocent, the above stories were made up, but the names kept real.

It's also interesting to note that "Interweb" seems to also be used to refer to filtered or limited Internet access, either through a transparent proxy or through some form of logging gateway.

"Interweb access is what ``consumers'' get shafted with in their homes as so-called broadband. Most corporations wire their employees' desks with Interweb access, even though the corporation itself gets an Internet connection from its ISP." (sakima.ivy.net)

References:
http://sakima.ivy.net/~carton/academia/internet-vs-interweb.html