3. Business jargon
Business jargon should not be present in a business letter.
More information:
Business jargon (or, corporate jargon) is a special language used by companies and management institutions. It usually includes buzzwords, vogue names, and euphemisms.
Business jargon is commonly used in large companies, at bureaucracies, and in similar workplaces.
But, it should not be used in business letters.