ying yang is a very important concept of chinese medicine and kung fu especially tai ji, and it is deep down in the chinese culture which you can find it in a lot of areas in life, that's why you can find the taiji symbol in your address bar of your browser when you browse my website.
ying yang, its definition in terms of human, kung fu, chinese medicine, etc.... ying could means female, soft, cold, etc.... yang could means male, strong, hot, etc.... chinese believe ying yang is the basic construction of human body, and you might notice there is a small black dot in the white part of taiji and vice versa, which means ying has yang and yang has ying, ying is the opposite of yang, but they exist together as a whole which is taiji, it seems like a contradiction, how could a male a female and a female a male, but let me explain this way, a male also have female hormone and a female could have male hormone. ying yang is a concept, it is about balance, when you are too ying or too yang, means your health is not at a good condition.