The story about Gin is just as long and exciting as with Whisky and it will take many hours to get it covered in a decent way.

But shortly, Gin today is defined by EU-regulations as a spirit with a minimum of 37.5 % ABV where the significant ingredient is Juniper. Gin is divided into 4 categories:

London Dry Gin: The botanicals are distilled with the last run.

Dry Gin: Essenses are added.

Plymouth Gin: Can only be made in Plymouth.

Old Tom Gin: How it was made in the old days.

You can read more about it here (Danish): "Enebær på flaske" or follow the blog which contains a lot of info in English.