Non-standard English, also written as nonstandard English, refers to use of English, especially regarding grammar, but also including other aspects of language, that is considered by convention to be sub-standard or not "proper".
That, however, does not mean it is not or cannot be used. Everybody, even the most punctilious language pundit out there, will at some moment of the day or his/her life "slip" into non-standard English, depending on context and company. In fact, the vast majority of the English language which we use today would certainly have been considered non-standard or incorrect at some point during the evolution of the language, and, to the horror of today's purists, today's non-standard may well become the Queen's English of tomorrow.
Perfectly correct regional variations of English may be deemed non-standard by certain people using a subjective barometer of what they, personally, and sometimes, in the case of those who consider themselves language pundits, vociferously, consider "correct".
 Examples of non-standard British English
The verb "to be" is the most complex in English, but some non-standard usages seem to be attempting to regularise it:
- we was is used in place of "we were". Especially by footballers, as in "we was robbed."
- if I was you is used in place of "If I were you".
- they was waiting for us is used in place of "they were waiting for us".
- ain't is frequently used - even if in a jocular vein - instead of (be) not (and also (have) not)
- innit = isn’t it? – It’s cold today, innit?
- I be is is used in place of "I am" in some regional accents.
 Register and "unrecognised" contractions
Then there is the question of register and unrecognised contractions. While some contractions such as "isn't" are recognised and acceptable in speech and informal written registers, others are acceptable in speech but frowned on in all written forms of the language, some include:
- gonna for (be) going to (first recorded in the OED in 1913)
- wanna for want to (first recorded in the OED in 1896)
- gotta for have (got) to (first recorded in the OED in 1924)
- don’t for doesn't - as in The Beatles song "Ticket to Ride": "she's got a ticket to ride and she don’t care."
- gotten is not used in British English but is very common in American English. It is interesting that the Compact OED somewhat snootily claims that "even there it is often regarded as non-standard" while the American Merriam-Webster simply notes its existence.
One form of non-standard language is slang. It is especially common in pop, rock, jazz and rap music, as well as in films, all of which tend to have international audiences, and many foreign speakers who have learnt more formal registers are sometimes surprised when they hear expressions like: “I gotta go!” (I have to go now). In certain regions, certain dialects may have this non-standard language incorporated into “normal” speech.
- C’mon! = Come on!
- cop = policeman
- ‘cos = because (first recorded in the OED in 1828)
- cuppa = cup of tea
- don’t = doesn’t – He don’t love me.
- dunno = don't know (first recorded in the OED in 1842)
- gimme = give me – Gimme my bag!
- kinda = kind of
- lemme = let me – Lemme see that book!
- lil’ = little – He’s gotta nice lil’ house in the country.
- lotta = a lot of – He’s gotta lotta money!
- luv = love (first recorded in the OED in 1898)
- ma = my
- OK = all right
- ol’ = old
- outta = out of – Get outta here!
- sorta = sort of (first recorded in the OED in 1790)
- Y’all = all of you
- yeah = yes
- wot = what (first recorded in the OED in 1829)
- wotcha = What are you ...? – Wotcha gonna do when you get there?
It is also quite common to hear or see words finishing in -ing in which the final g is substituted by an apostrophe. Examples include the upper class expression huntin', shootin' and fishin', and the lyrics of pop and rock songs: cryin’ – drivin’ – dyin’ – livin’ – lyin’ – rockin’ – singin’ – sittin’ – talkin’ – walkin’ – etc.
Jargon is the common vocabulary used by specific professions or groups of people within those professions. It can be similar to slang or it can be highly technical: legal jargon; medical jargon; police jargon;