What is the main difference between envelopes and letterheads?

Answer 1

An envelope is a packaging item. I.e. you use an envelope to mail a letter

A letterhead is a heading that is on top of a paper. Usually has name, company name, address, telephone number, etc.

Answer 2

Envelopes are used to enclose and protect documents when sending them through the mail, while letterheads are a printed heading on stationary that typically includes a company's name, logo, and contact information. Envelopes provide a protective covering, while letterheads are used for branding and professional correspondence.