Cockney is the dialect of the Londoners (officially only people born within the sound of the bells of Bow church - as in the rhyme "Oranges and Lemons").
It's the accent of Tommy Steele (in Half a Sixpence), Aliza Doolittle, and what Dick Van Dyke did so risably and execrably badly in Mary Poppins (he's still fondly remembered here for his "Cor Bloimey Mary Porppins!".
Anthony Newley used to sing in a cokneyesque manner (emulated by the early David Bowie - "Graound controwl to mijer Tom..."

Essentially, it's the sort of accent that most Americans associate with a Brit, and what most approximate when they try to do a "British accent" (there's millions!) - "Allow Mite" (hello mate)

Strangely, in Frasier, when Daphne's drunken brother came over from England (played, I think, by the guy from that FBI "Missing..." programme), he sported a "mockney" accent, even though he was supposed to come from Manchester, like Daphne, and thus sounded absolutely ridiculous.

I've never heard an American actor yet who can faultlessly carry off any British accent; the most common mistakes are:

Words that a "posh" or southern Brit would pronounce with an "ar" sound, e.g. "past" is like "parst" - end up like "aaaa", as in "paaaast"

Inflexion on words, e.g. "inquiry": US "IN-quiry" - GB "in-QUIRE-y"

The rolling Rs, e.g. Posh Brit says "girl" as "gehl" or "gehrl", US - "grrrrrrrl"

One of the best attempts, almost perfect, was Gwyneth Paltrow in "Sliding Doors"

:-)


>So, is cockney a dialect? Like saying mid-western or southern, here?
>
>>Exactly, just as I explained in the brackets. Quite often Brits say "Blimey". Another antiquated cockney one you might have heard (on stereotypical British films say - e.g. B&W war films) "Lummey" (corruption of "love me"). Hence "Cor lumme" (or "Gor lumme") :- "God love me"
>>
>>>What does blimey mean? Is that the derivation if blind me? Some County Cork friends of mine used to say it fairly often. Well, that and a few others that wouldn't mean much here in the States, but would in Europe.
>>>
>>>>(cockney) Gorblimey (corruption of God blind me)