Brit. ~n. (1) a person who comes from or lives in Tyneside, North Eastern England. (2) the dialect spoken by these people. ~adj. (3) of or relating to these people or their dialect. (Taken from the Collins English Dictionary.)
What else can you tell me?
You pronounce Geordie as: "jaw-dee" (jaw as in 'jaws', and dee as in 'deep'), and there are four possible explanations for the name Geordie. It would appear that no-one knows which is correct, if any;
 One opinion is that the name was born in the Jacobite Rebellion of 1745, when the Jacobites bypassed Newcastle, which, as well as favouring the Hanoverian King George, was also a well-guarded garrison. The Jacobites then said that Newcastle and the surrounding areas were all "for George" - hence the name Geordies.
 Another school of thought thinks the name originated from the coal mines of Durham and Northumberland, for many poems and songs written about, and in the dialect of these two counties, speak of the Geordie. The Oxford English Dictionary states that the word has two meanings: a guinea (which had the figure of St. George on it) and a pitman. Whilst the name was applicable to coal-miners it later became applicable to Tynesiders in general.
 The third possible origin is from George Stephenson, who in 1815 invented the miners' lamp. The Northumberland miners used this lamp in preference to that invented by Sir Humphrey Davy at the same time, and the lamp (and eventually the miners themselves) became known as Geordies.
 The last possible explanation also derives from George Stephenson. In 1826, he gave evidence to a Parliamentary Commission on Railways at which his blunt speech and dialect drew contemptuous sneers. From that date, it is said that Londoners began to call the Keelmen, who carried coal from the Tyne to the Thames, Geordie.
So who is permitted to call themselves a Geordie?
Again, there are various viewpoints. Originally, it would appear that the name applied only to miners [origins 2 and 3], Keelmen [origin 4] or inhabitants of Newcastle [origin 1]. Later it became applied to members of the Tyneside Community at large. Nowadays, it would seem that anyone in Northumberland, Durham or Tyne & Wear can call themselves a Geordie!
(Taken from Newcastle upon Tyne City Libraries & Arts - local fact sheet 5)