What is the paris convention and What are the principal features of the paris convention?
A brief answer is that the Paris Convention was an international agreement (dating back to the late 1800's) wherein participating countries respect the priority date of patents (and some other forms of IP as well) first filed in other participating countries.
So an inventor filing a patent in America, for example, would have up to 12 months to file the same patent in Germany, and the German patent office would grant this patent the same filing date as the original US application. This is important in order to establish who invented first.
The Paris Convention is still in effect, but there is a later treaty, called the Patent Cooperation Treaty (PCT), to consider as well. Under the PCT if you file a PCT application within 12 months of your first filing, the PCT will extend this mutual respect of priority dates to up to 30 months from the initial filing date.