WHOA! Great question and although most will offer up one term or another - it is a sure bet that something else has more searches. Start with searching terms relative to your needs.
The highest searched word I've ever come across wasn't a term rather - the letter 'a' @ 1.68 BILLION per month. That could be a result of many factors though. For a whole term - 'YouTube' leads the way with 1.38 BILLION searches per month.
Facebook was the most commonly searched term on Google in the year 2012. Close behind were youtube and hotmail.
ronaldo
It is "google."
Check out "Google Trends" to view an up-to-date record of Google's most searched keywords.
Why? Is the most asked question.
dirty sex jokes
I'd say google.
The most typed word in Google search is "sex". In a 2010 analysis.
Google is most popular search engine in the world
Pregnancy is the most widely searched health term, followed by cancer.
Currently Google, but in the U.K the most searched engine site used is Facebook, followed by BBC.CO.UK
the biggest I've found so far is "free", but there might be a more searched one out there...