A "stroker" is a motor in which the cubic inch displacement (cid) has been increased by increasing the stroke length. There are three factors that determine a motors cid. One is the number of cylinders, in our case, 8. The second is the bore which is the diameter of the piston. The third is the stroke which is the distance that the piston travels up and down.
Stroker motors require a complete rebuild as the crankshaft, pistons, and connecting rods are all swapped. They are not a simple bolt-on mod.
The two most common cid stroker kits for the 5.0L are the 331 (4.03" bore x 3.25" stroke) and 347 (4.03" bore x 3.4" stroke).