The full form of weeb is weeaboo
The slang term “weeb” is a descriptive term that is used humorously or as a serious insult to describe someone obsessed with Japanese culture. It is an abbreviation of the full term “weeaboo.”

Origin of Weeb
The term “weeb” was first used on a social media site known as 4chan. It was first recorded being used on Twitter in 2010 and on other sites in 2011 and 2012. A search of Google reveals that the term was first used in 2011. It is most often used on social media and other sites as a derogatory term to describe a person who is obsessed with anime or manga and the Japanese culture, so much so that they believe the Japanese culture is superior in many ways to their own.

Other Meanings
A search of the term “weeb” will reveal that there are many other meanings of the term “weeb.” However, there are too many to list them all here. Some of the other meanings include a slang term for “dick,” a stupid or weird person, an alternative term for the word wig, a creature that is sub-human, a person that no one likes, or the name given to the penis of a monkey or any other type of primate.

Example Conversations
A text discussion between two friends.

Friend 1: I like Tony and all, but he is such a weeb!
Friend 2: I think you mean dweeb, as in nerd.
Friend 1: No, I mean weeb. He is obsessed with everything Japanese from anime to learning the language.
Friend 2: Oh I see what you mean and agree. I think he would rather be Japanese as much as he talks about it.