The 1500 in a Dodge truck name doesn't relate to any particular specification, such as engine size, cargo capacity or wheel base, but it does help differentiate this model of truck from other Dodge truck models.
Dodge manufactures three sizes of full-size pickup trucks, with each size based on cargo capacity and towing power. The smallest of these is the 1500, the intermediate size is the 2500 and the largest truck is the 3500.
Trucks used to be classified by the amount of weight they were able to haul. A half-ton would carry 1,000 lbs., a three-quarter-ton would haul 1,500 lbs. and a 1-ton would haul 2,000 lbs. Those ton-designations are still assigned to pickup trucks, though modern trucks will easily carry more than their designation implies. A Dodge 1500 is listed as a half-ton truck, but has a carrying capacity of 1,900 lbs.
Dodge offers myriad options and option packages for all of its pickup trucks. They come in two-wheel-drive and four-wheel-drive options, various cab styles and cargo bed lengths. Just remember that when you see the 1500 number in the model name, it indicates it's the smallest of the three sizes of Dodge's full-sized pickups.