What is the SECOND biggest search engine in the world?

Youtube !!

Read following articles:

- http://www.socialmediatoday.com/content/second-largest-search-engine-infographic

- http://www.mushroomnetworks.com/infographics/youtube---the-2nd-largest-search-engine-infographic

I would say Youtube and Wikipedia. You can even do keyword research using wikipedia.

Search engines can be very centric to a particular country like Baidu in China, however as a whole Bing is the second largest search engine in the word that functions in most of the countries.

Bing

YouTube is the3rd biggest site in the world in terms of traffic and is the world Top Video search engine.

Yahoo is the4th biggestest site site in the world in terms of traffic and is a proper search engine. So your answer will be any of the ones you like. 

Google has become an integral part of my daily life, offering a suite of services that streamline everything from search to communication. The seamless integration of Google services simplifies tasks and enhances efficiency. Exploring google reviews, I've noticed a consensus among users, praising the reliability, innovation, and user-friendly nature of Google's offerings. It's evident that Google continues to be a trusted and invaluable companion for countless users worldwide.

Baidu is the second largest search engine in the world which has almost10% search engine users around the world.

YouTube - The2nd Largest Search Engine (Infographic) YouTube processes more than3 billion searches a month.100 hours of video are uploaded every minute. It's bigger than Bing, Yahoo!, Ask and AOL combined!

YouTube definitely.