What is slang (eg please)?

"Slang is the use of highly informal words and expressions that are not considered standard in the speaker's dialect or language."

"Few linguists have endeavored to clearly define what constitutes slang. Attempting to remedy this, Bethany K. Dumas and Jonathan Lighter argue that an expression should be considered "true slang" if it meets at least two of the following criteria:
- It lowers, if temporarily, "the dignity of formal or serious speech or writing"; in other words, it is likely to be seen in such contexts as a "glaring misuse of register."
- Its use implies that the user is familiar with whatever is referred to, or with a group of people who are familiar with it and use the term.
- "It is a taboo term in ordinary discourse with people of a higher social status or greater responsibility."
- It replaces "a well-known conventional synonym." This is done primarily to avoid "the discomfort caused by the conventional item [or by] further elaboration.

An example would be "getting a pop, meaning getting a haircut, or buying threads as in buying clothes."
Slang should be distinguished from jargon, which is the technical vocabulary of a particular profession. Jargon, like many examples of slang, may be used to exclude non–group members from the conversation, but in general has the function of allowing its users to talk precisely about technical issues in a given field."
Source and further information:
http://en.wikipedia.org/wiki/Slang

e.g. Here in New Zealand (kiwiland)
~A balls up = mistake
~Pissed/Blotto = drunk
~Boot = Car trunk
~Chilly Bin = cooler box (esky?)
~Nick/Flog = Steal
~Gidday = Hello (Good day)
~Sussed = Understood

Slang is common and casual language. It is used to make you sound friendly. Some examples are: "Mate" "Cheers" and common saying and words like those.

Anime Geek Slang

Narutard (people who show up to anime conventions with only a Naruto headband and their normal clothes with no original character)

Squeaky (person too happy/self-righteous to be real I.E. Ned Flanders or a Stepford Wife)

Some slang from my friends:
fly, bad, phat = cool

It is a saying,a fad word or style of speach that represents who you are which can change depending on the times or people with which you associate .