A "Memorandum" is best described as a type of -

• A "Memorandum" is best described as a type of - Formal letter.

• Letter দুই প্রকার। যথা -
i) Informal Letter : যা ব্যক্তিগতভাবে আত্মীয়স্বজন বা বন্ধুবান্ধবের কাছে পাঠানো হয়।
ii) Formal Letter: Official বা Business সংক্রান্ত চিঠিপত্র। যেমন - Application, Memorandum ইত্যাদি।
- সুতরাং, “Memorandum” is one kind of - Formal Letter.

• Memorandum:
1. a short note written to help one remember something or remind one to do something/ a record of events or observations, esp. one for future use.
2. an informal written communication, as from one department to another in an office
3. In diplomacy - a summary or outline of a subject under discussion, reasons for or against some action, etc.
4. In Business - a statement, made by the consignor, of the goods and terms of a consignment sent with the privilege of return.
5. Law - a short written statement of the terms of an agreement, contract, or transaction.

Source: Collins Dictionary.