Wire transfer transparency is the policy goal behind what is more commonly called the Travel Rule, and that entry explains the rule in detail. This page explains the term and where it comes from.
The idea is that every wire transfer should carry accurate information about who is sending money and who is receiving it, and that this information should stay with the payment as it passes from the originator's bank, through any intermediaries, to the beneficiary's institution. That allows each institution to screen the parties against sanctions lists and monitor for suspicious activity, and lets authorities trace funds later. The international standard is FATF Recommendation 16 on wire transfers, which sets the information required and the duties of ordering, intermediary and beneficiary institutions, including what to do when information is missing.
The names differ by audience. Standard-setters and banking associations speak of wire transfer or payment transparency, stressing the quality of data in payment messages such as SWIFT MT103 and ISO 20022 formats. "Travel Rule" comes from the US rule on passing information with funds transfers, set out next to the funds transfer recordkeeping rule, and is now also used for transfers of virtual assets under the FATF Travel Rule. Removing or altering party details to avoid screening, sometimes called wire stripping, breaches these rules and has led to major enforcement actions.