Te (as spelled using Wade-Giles transliteration) or De (using pinyin transliteration) is translated and interpreted in so many different ways, even within Taoism, that it is quite difficult to come to a clear understanding of the concept. Confucianists and Zen Buddhists will sometimes impose their philosophies on the concept when referring to Taoism, further making the process of discernment difficult.
That written, I hope this does not further confuse things...
The two most popular translations for Te are "virtue" or "power," words just about as ambiguous in English. "Virtue" as the morally correct way to behave is more Confucian. "Virtue" in the sense of a "quality" comes a bit closer. "Power" is close if we think of it as "the power of Tao" and not as our personal power. There is a uniquely personal aspect to Te as well, however.
Where the Tao Te Ching (Dao De Jing) and Chuang Tzu (Zhuangzi) -- the two main texts of Taoism -- describe Te, one gets two senses of the concept. It is, on the one hand, the way that Tao expresses itself in us and each of the ten thousand things (our talents, our preferences, our physicality, our emotions, our thoughts, and our other unique traits). On the other thand, it is a state of being that allows one to connect with Tao, and in that sense it is something that is not so fixed; it is something we can develop. Here is how the two texts use the term:
Chuang Tzu then goes on to show other ways in which the sage exhibits Te or Virtue, using "Heaven's Virtue" as another name for Tao:
Lao Tzu talks more of Te being one's original nature, suggesting in the following quotation that the longer one remains in harmony with Tao and one's original nature (before the influences of fear and knowledge among other things), the more freedom one will have to achieve great things with very little effort:
Lao Tzu holds the infant as the highest example of Te:
Lao Tzu goes on in the same chapter to suggest the consequences of losing one's Te: