A letter is anything you write to anyone. A memorandum is a reminder, generally about protocol or directives, that's written to employees or clients.
a circular is a circle duhhh!!
A Memorandum of understanding is the more formal of the two and is used to discuss an agreement in a broad spectrum outlining the overall goal so it is clear whereas the Memorandum of Agreement...
"Memoranda" is the correct plural form of "memorandum."
They are the same. There is no difference.
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