I tried to figure this out when someone asked this same basic question a few months back, but gave up when I couldn't find a sensible explanation online.
This set of paranoid, nonsensical replies has made it imperative that someone provide a realistic response though, so I took another pass at figuring this out.
After an initial search where I found someone took a stab at a sensible generic response in Yahoo Answers as follows:
What does guccounter=1 mean Yahoo Answers
At this point I noticed something in several of the other Bing research results and changed my next search to simply the following:
https://www.bing.com/search?q=yahoo.com%20%22%3Fguccounter%3D1%22&qs=n&form=QBRE&sp=-1
If you ignore the formatting garbage between fields and near the and, you'll see I simply searched for Yahoo.com and "?guccounter=1", which gave me a list of many of the top level Yahoo pages like My Yahoo, Help for Yahoo Account, Yahoo Answers, Yahoo Maps
and others, each containing the "?guccounter=1" portion appended to the end of the URL.
So quite clearly, this is simply some sort of command that probably increments a counter related to that specific page in order to record how often that particular link is used.
Computer code seems to have some sort of mystical property in the modern world, probably due to the fact that so few actually know what the specific purpose for most of it truly is, so many people start to create a mythology in order to try and explain it.
In many cases as with religion the result is a nonsensical statement of "fact" that many begin to accept as "gospel", when in truth it's simply a confused group of people creating a set of beliefs that are accepted due to "groupthink".
"What Is Groupthink?
Groupthink occurs when a group with a particular agenda makes irrational or problematic decisions because its members value harmony and coherence over accurate analysis and critical evaluation. Individual members of the group are strongly discouraged from any
disagreement with the consensus and set aside their own thoughts and feelings to unquestioningly follow the word of the leader and other group members."
Computing today is full of groupthink and thus mythology as well, so much so that it's hard to find any real facts within the mess on many supposedly technical forums any longer.
I learned computing from simple books written by people like Adam Osborne and others from the early days of the microprocessor and microcomputer. Today most people learn from their friend, neighbor or the kid down the street, so is it any wonder that a mythology
has developed as a result?
Code is written by people who often try to write it in ways that make it obvious and easy to understand and remember. So try to read it that way and you'll often find relatively obvious reasons for the naming of items within the code. Unless, of course,
the writer is a malicious actor who's trying to obfuscate what's being written to hide its true purpose.
Rob