Simplify the following text for a Grade 6 native English-speaking person.
Original: The term ZIP , an acronym for Zone Improvement Plan , is properly written in capital letters and was chosen to suggest that the mail travels more efficiently , and therefore more quickly , when senders use the code in the postal address .
Simplified: The letters are written properly in capital letters . The word ZIP was chosen to suggest that the mail travels more efficiently , and more quickly , when senders use it .