Tai chi ch'uan is a slow motion self defence art based on Daoist principles. The meaning of the word is supreme ultimate fist. The translation may be limited, but does go some way to explain things.
The word chi above is different to the word chi or ki meaning breath. Again, the translation into English hide much of the original meaning.
Another concept is the notion of being double weighted. Again, not much hope of grounding this term in English without some other input. Double weighted is a state in which you can move with ease, it is a state of stuckedness... that is you are stuck in one position and cannot easily get to the next. This can be a physical or a mental state - a rabbit staring into the headlights of a car is double weighted.
Is this clear? Probably not. Tai chi is experiential, so only by practice and a little discussion can we start to understand.