Singlish is a bastardisation of the English language, named after the country in which it was "invented" and commonly spoken, Singapore.
While many would say, as manifest has, that it is disgusting and sounds extremely coarse, I would hold that it does have its uses. To Singaporeans, at least, it sounds intimate and informal, a social language that brings more people to ease.
While Singlish does have large Chinese (particularly Hokkien) influences, it also retains a certain Malay favour. Quite a few words of Malay origin are interspersed in speech.
There are two main defining aspects that qualifies a passage of text as Singlish.
The first would be the use of Chinese sentence structures in English. Take, for example, "Is this your one?". In proper English, this would be expressed as "Is this yours?", but because there is no such word as "yours" in Mandarin, "your one" is used, being a nearly direct translation of the Mandarin equivalent. (The word "one" is replacing has no true English translation; it is used as a suffix to denote 'belonging to'.)
The second aspect of Singlish is the use of strange suffixes and non-English words. The suffixes are perhaps the most famous, so I will go through them first.
In Mandarin, it is quite common to end a sentence or a phrase with a certain suffix, as an indication of tone. For example a question is normally suffixed with "ma", an exclamation with "ah" or "ya".
This is also done in Singlish, but in a much more extreme manner. While you would attempt to use the suffixes in a more restrained manner when conversing in Mandarin or other dialects, in Singlish nearly every other word has a suffix appended to it, and each suffix greatly influences the meaning behind the entire sentence.
The 8 most common suffixes are these: lar, lor, liao, leh, mah, meh, har, hor.
Example time.
"It's mine lar."
"Yes, yes, its mine, you can stop asking now."
"lar" creates a feeling of very slight annoyance in response to a query.
"It's mine lor."
"Yeah, its mine."
"lor" indicates nonchalance, as if the speaker is not really interested in the question. It can also be used when the answer is so obvious it need not be mentioned at all.
"It's mine liao."
"I just made it mine a while ago, so yes, its mine."
"liao" retains the same meaning as the Mandarin word of the same sound. Indicates something that has happened in the past, that there has been a completion of a task of sorts.
"It's mine leh."
"Hey, its mine!"
"leh" is used when countering a previous statement. In the example above, the sentence could be used after somebody else mkes claim to the object in question, or when the person speaking originally believes the object to belong to someone else, and suddenly realises it is his. Use of "leh" usually means that somebody is wrong somewhere.
"It's mine mah."
"Yup, it's mine, that's why I'm taking it home."
"mah" is similar to "lor" and can sometimes be used interchangably. However, it is used when the statement is an explanation, and does not carry the I-couldn't-care-less feel that "lor" implies. It does express that the speaker believes this explanation is good enough for the listener and no further elaboration is required.
"It's mine meh?"
"Huh? It's mine? Are you sure?"
"meh" is identical to the Mandarin "ma" mentioned earlier. It is used to suffix questions, with the added suggestion that the speaker is in a state of disbelief.
"It's mine har."
"This is mine, it belongs to ME."
"har" stresses the importance of the sentence, in a "don't you forget it" manner, without the hostility.
"It's mine hor?"
"This is mine... I think. Do you think so too?"
"hor" has three meanings. When used in a query, it is suggesting to the listener that an acknowledgement is required.
When used at the end of a sentence, it is generally identical to "har", except it is slightly more hostile ("This is mine hor, don't touch it!").
When used in between phrases ("So hor, he climbed up the stairs hor, and then opened the door"), its meaning is a bit hard to describe. Think of it more as a transitive sound, such as the "eh" and "hmm" that are used in English at times.
Of course, since these suffixes are not actual words, they have no true fixed meaning. The explanations given come close to the mark, but the best way to determine what a speaker is implying would still be through the tone and inflexion of the whole sentence; and remember that sarcasm is used quite often as well.
As mentioned above, many foreign terms are typically inserted into a Singlish sentence. The most common ones would be Hokkien exclamations, like "wah lau" and "wah biang". These are all minor expletives in Hokkien, but have lost their real meaning in Singlish; they are roughly equivalent to English phrases like "Oh my god".
Other languages appear occasionally as well, depending on the ethnicity of the speaker. A man of Chinese blood would probably substitute various nouns or adjectives with the Mandarin equivalent from time to time, while an Indian may use Tamil in a similar manner.
However, there appears to be a common pool of phrases that all races use. The Hokkien terms mentioned above are a few of them; others include Malay words such as "alamak" ("oh no") and "balik" ("go back"). Almost everybody knows what these words mean.
I am no linguist, and have never carried out any formal research into this particular brand of English. These are all merely my personal thoughts and understanding of the sub-language that I have grown up with, so remember to take it with a grain of salt.
Warlau... thanks for all the cools man, one simple writeup about Singlish also can get so good response, damn shuang ah! So I give you all a bit of Singlish lar, let you all try try see if can figure out the meaning or not. Fun hor? Abuse of language is always very the hao wan one...