Slang and Colloquial?

'colloquial' simply means the language that is used in everyday speech. Another name for it is nonstandard English. It's not the best name in that it is highly misleading. It has caused many people to consider it substandard English, even incorrect or bad English, which it most certainly is not.

The notion that the language that all speakers use for the vast vast majority of their English is wrong/bad/incorrect/substandard is a completely ludicrous notion.

The rules for nonstandard/colloquial/informal English are different rules than those that apply to Standard Formal/Written English. Speech is primary to language. From it flows all language change.

Though speech and writing share many of the structures of the English language, many of the rules that govern writing are artificial constructs. Many are outright falsehoods, perpetuated by people who know/knew little about the workings of language.

'slang' is new language. Because speech is primary to language, all "slang" comes from speech. It consists of new words and meanings. It is found, for obvious reasons, within informal/colloquial speech. Often, slang is limited to a particular group. It's not really a stretch to consider all the new terminology surrounding computers to be slang.

'slang' has a bad reputation. This is undeserved of course but it's natural that people often find changes to language that they don't understand distressing.