Question

what do you mean by report and letter​

Answer 1

Answer:

Reporting letters support client communication by describing the work that has been completed and the results achieved.

A letter is a written message conveyed from one person (or group of people) to another through a medium

Answer 2

letters are generally used when a person has a specific issue to communicate. Reports, on the other hand, may be used in conjunction with making a specific decision, but they may also be compiled simply to share information about a project.
Another explanation is -
report is a piece of information describing, or an account of certain events given or presented to someone while letter is a symbol in an alphabet, bookstave or letter can be one who lets, or lets out.