The MSPE (Medical Student Performance Evaluation), sometimes called the Dean's Letter, is a summary of a student's academic performance, clinical evaluations and professional attributes that a medical school prepares for the residency application. In ERAS it is released to programs on a set date.
Not every international school produces an MSPE in the same format, and practice varies. If your school does not, ask what document it provides and check how programs treat it. See the ERAS entry for where it fits in the application.