A program is a user-made file that performs a specific function on the calculator. They are made in a language called TI-BASIC. Applications on the other hand are most often created by TI itself and are created in a different language called Assembly, which is a lower level language that lets the user do anything the calculator can do. Applications are generally more graphical and larger than a program. Programs, however, can also be made in assembly. It is possible to purchase a signing from TI to have them turn your assembly program into an application, but few people do this.