I realized that most of the people that I know closely don't know what Transhumanism is. So here is my very diluted and basic definition. Transhumanism is the use of technology and knowledge to help improve the human condition.
If you want to know more, there are large communities online that philosophize about what new technology trends may portend for the future of mankind. They also have basic documents that explain the basics of what their group considers to be the core of Transhumanism.
Humanity + (H+) has this called the Transhumanist Declaration. It can be considered the founding statement of what transhumanist believe and aspire to. It is very open ended and focuses on the responsibility of using technical progression wisely.
The Mormon Transhumanist Association (MTA), which I belong to, has this to say in their Mormon Transhumanist Affirmation.
The end goals of both of these groups are for humans to use technology to transcend our current state. There are many different opinions on how it is going to play out and what methods will be used, but most agree that technological changes are accelerating and compounding. As knowledge itself is not good or evil, it is up to us to choose how to use it.
For me, the choice is clear. I need to live this life authentically and actively.