AISI 304 is used in a variety of household and industrial applications.  304L is an even lower carbon version of 304 stainless steel and can be used in more corrosive environments such as salt water and chemical containers.  Both 304 and 304L can be used in the welded condition as opposed to the annealed condition and still maintain resistance to corrosion and lend themselves to many types of fabrication.  These grades resist corrosion and are often used in the food industry.

304L: % C≤0.03   Si ≤1.0   Mn ≤2.0    Cr 18.0～20.0 ,  Ni 8.0～11.0,  S ≤0.03  P ≤0.035
304: % C≤0.08   Si≤1.00   Mn ≤2.00   P≤0.05   S≤0.03   Cr 18.00-20.00  Ni 8.00~10.50

The big difference between 304 and 304L is the Carbon percentage, 304L carbon percentage below 0.03%, while 304 carbon percentage below 0.08%.