One of the major differences between lemon and citron can be seen when you consider the quantity of juice you can derive from each fruit. Those who are familiar with the two fruits know lemon has more juice compared to citron. Another difference between the two is that; although the two fruits are used for medicinal purposes, however, the citron was formerly being used for these purposes.
Aside from these little differences, citron and lemon are similar in the sense that they belong to the same family, i.e., the citrus family. Also, in terms of what they are used for, there is no big difference between the two.
For instance, aside from the fact that they have certain medicinal values, they are also used in making products like perfumes, oils, flavorings, etc. Also, both have similar tastes. However, what could also be a difference is that the two fruits can't be substituted for all kinds of foods.