Difference between transactions and journal I feel a little bit ashamed, but I have never understood the difference between transactions and journals. This question is quite related. However, I could not find any clear differentiation.
For example, in my little field (software engineering) IEEE Transactions on Software Engineering is considered the top venue. However, there is not an IEEE journal on Software Engineering (or whatever name). To be honest, I have never seen any publisher on software engineering having both transactions and a journal on software engineering. This is also why I fail do differentiate them.
This is what IEEE writes at its FAQ page.

What is the difference between IEEE Journals, Transactions, Letters, and Magazines?
Journals, Transactions, and Letters are the primary means for
publishing technical papers concerning original work in IEEE fields of
interest. [..] The primary purpose of
Journals, Transactions, and Letters is to disclose and provide a
permanent archival record of original technical work that advances the
state of the art or provides novel insights. Papers in Journals,
Transactions, and Letters should be of lasting value to the
professional as judged by the authors’ peers through a formal review
process. [..]

The omitted part is about letters and magazines, so it is not related. Am I really missing it, or they do not really differentiate?
What is the difference?
Transactions used to have a very specific meaning. From the New Oxford American Dictionary:


  transactions
  published reports of proceedings at the meetings of a learned society


In this historical usage, it is synonymous to proceedings, i.e. it is a published report of a conference or a set of meetings. Many learned societies have transactions: Philosophical Transactions of the Royal Society, Transactions of the Faraday Society, Transactions of the AMS, etc.. Some other institutions use the term “proceedings”, e.g. Proceedings of the National Academy of Science.

These transactions or proceedings were separate from journals, which do not have to coincide with a conference or meeting. However, with time the customs changed, and many of these reputable publishing venues became independent from actual meetings or conferences. But, because they were reputable (and famous is some cases), the name remained.