What is the difference between letter, communication and journal paper? Scientific literature has items called letters, communications and journal papers. They all seem quite similar in terms of format and content. What are the differences between them?
In physics, each category has a different length limit.  Often "paper" has no limit.  Typically the shorter the length limit, the more prestigious it is and the tougher the acceptance criteria.  The subject matter covered by the journal is the same for all categories.  Some journals also have a "review" category which includes papers which are not original research.  Often a review is by invitation only.