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 hand, 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:
"To achieve loftiness without the burden of bias;
to follow the ways of improvement without benevolence or righteousness;
to rule successfully without achievement or fame;
who rest without rivers and oceans;
long life without organization;
to lose everything and yet to have all;
to drift calmly and endlessly, while all good things pay court to them;
this it the Tao of Heaven and Earth, the Virtue of the sages."
-- from The Book of Chuang Tzu, Palmer (tr.), p. 130
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:
"The saying goes, 'Calm, detachment, silence, quiet, emptiness and actionless action, these are what maintain Heaven and Earth, the Tao of Virtue.' The saying goes, 'The sage rests, truly rests and is at ease.' This manifests itself in his calmness and detachment, so that worries and distress cannot affect him, nothing unpleasant can disturb him, his Virtue is complete and his spirit is not stirred up.
"The saying goes, that the sage's life is the outworking of Heaven, and his death is the transformation of everything. When he is still, his Virtue is like yin; when he is moving, his pervasiveness is like yang. He brings neither good fortune nor bad. He acts and moves in response to forces beyond. When he finds something, he rises up. He ignores knowledge and nostalgia, following only the pattern of Heaven. So he risks no disaster from Heaven, nor complications from things, no accusation from anyone, no charges from the spirits of the dead. In life he floats; at death he rests. He does not consider and plot, nor design for the future. He shines but is not seen; his good faith has no record; his sleep is dreamless and he wakes without fear. His spirit is pure and without blemish; his soul never tires. Empty, selfless, calm and detached, he is in harmony with Heaven's Virtue.
"It is said that sadness and happiness are corruptions of Virtue; joy and anger are errors of the Tao; goodness and evil are contrary to Virtue. So, for the heart to be without sadness and happiness, is to have perfected Virtue."
-- from The Book of Chuang Tzu, Palmer (tr.), pp. 130-131
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:
"In governing people and serving heaven,
Nothing is better than being sparing.
Being sparing is called early adherance [to Tao].
Adhering early is called being heavy with accumulated te.
To be heavy with accumulated te,
Then [such a person is] all overcoming.
Being all overcoming, then there is no knowing the limit."
-- from the Tao Te Ching, chapter 59, E. Chen (tr.)
Lao Tzu holds the infant as the highest example of Te:
"One who contains te in fullness,
Is to be compared to an infant.
Wasps, scorpions, and snakes do not bite it,
Fierce beasts do not attack it,
Birds of prey do not pounce upon it.
Its bones weak, its sinews tender,
But its grip is firm."
-- from the Tao Te Ching, chapter 55, E. Chen (tr.)
Lao Tzu goes on in the same chapter to suggest the consequences of losing one's Te: