A leaky acronym is an acronym used in partially expanded form, with the acronym itself left intact. The canonical example is “PIN number”: The “N” in “PIN” stands for “Number”, but the acronym has leaked and you’re really reading “Personal Identification Number number”. Some earth-dwellers call these “redundant acronyms” but Avaragado prefers to call them “leaky acronyms”, and so do you.
More specifically, in Avaragado’s superior terminology, “PIN number” is a Post-Leaky Acronym. It’s “Post” because the acronym leaks from the right-hand end. Another example is “WTS Server” (Windows Terminal Server Server).
You can also get Pre-Leaky Acronyms, such as “Acorn ARM” before the A was retconned into Advanced a hundred years ago. Avaragado is pretty sure there was a “Tarantella TSP” somewhere in the web site of a former employer.
Some Avaragado acolytes have spotted Mid-Leaky Acronyms: “Intel IA64 Architecture” leaks both the I (pre-leaky) and the A (mid-leaky).
The ultimate leaky acronym occurs when you have complete acronym breakdown, such as with the hugely leaky “Surface-to-Air SAM Missile”.
Other examples:
- Built on NT technology – NT stands for New Technology (allegedly). This particular example
- occurs in the Windows 2000 login screen.
- HIV virus – Human Immunodeficiency Virus virus. Probably as popular a leaky acronym as PIN number.
- ATM machine – Automated Teller Machine machine.
- LCD display – Liquid Crystal Display display
- TCP/IP protocol – Transmission Control Protocol/Internet Protocol protocol.
- HTTP protocol – Hypertext Transfer Protocol protocol.
- FAQ question – Frequently Asked Question question.
- RAID array – Redundant Array of Inexpensive Disks array. Ooh, mid-leaky!
- PERL language – Practical Extraction and Reporting Language language.
- PAC code – Porting Authorisation Code code.
Avaragado would be delighted to receive more examples to add to his collection.
Avaragado's blog 
My employers annoy me by referring to Lloyds TSB Bank – meaning that all of our official correspondence comes from Lloyds Trustee Saving Bank Bank.
Luckily, we appear to be collecting fragile financial institutions like a greedy rent boy collects STIs, so nowadays, the internal correspondence uses the overarching and more sensible moniker of LBG (Lloyds Banking Group).
There’s one in “LloydsTsb bastards”, the stupid bastards.
Someone in the pub has sugested UKIP Party