The difference has always stumped me, so I did some research today. So important, so amaze, so wow, Mrs. Wagon.

According to Wikipedia:

In American Chinese cuisine, an Egg Roll is a savory dish typically served as an appetizer similar in concept to what is commonly known as Spring Roll in Asia but made with flour dough wrap instead and deep fried or baked resulting in a crispy product. Egg Roll is usually stuffed with pork, shrimp, or chicken, adding cabbage, carrots, bean sprouts and other vegetables, and then deep fried.

So basically, the Spring Roll is the smaller one with the thin, crispy, whitish wrapper and the Egg Roll is the bigger one with the thick, bubbly, deep-fried outer layer. The fillings can vary based on whoever is filling it...!