Finally I find the explanation of what Bodhisattva means; the short explanation is 菩薩(Bodhisattva) 就是覺有情: 覺悟的一個眾生，他不迷了 – 是「諸惡不作，眾善奉行」; in English: A Bodhisattva is also defined as “an enlightened sentient being.” The Bodhisattva is the same as other living beings, except that he is enlightened. Being enlightened, he “does no evil and practices all good deeds. Source: 藥師琉璃光如來本願功德經淺釋 Sutra of the Merit and Virtue of the Past Vows of Medicine Master Vaidurya Light Tathagata with Commentary
「菩薩」這兩個字，我們就應該知道，這是大乘裏邊一個聖人。菩薩也是半梵語，具足就叫菩提薩埵，英文又叫 Bodhisattva ，翻譯到中文，它就叫覺有情。有情就是眾生之一，菩薩是九法界眾生之一，也是四聖法界裏邊一個聖人。怎麼叫覺有情呢？就是說他用這個覺悟的智慧，來度脫一切的有情眾生。有血有氣的都叫有情；沒有血沒有氣的，那叫無情。好像一切的植物，這叫無情，可是無情它們都有性，它們都在佛的大光明藏裏邊來生長，所以雖然是無情，可是有性。
English version of the above quote:
A “Bodhisattva” is a sage of the Great Vehicle. The full Chinese transliteration of the Sanskrit term is putisaduo, but the Chinese use the abbreviated form pusa. “Bodhisattva” means “one who enlightens sentient beings.” Bodhisattvas are one of the nine Dharma Realms of living beings and also one of the Four Dharma Realms of Sages. A Bodhisattva uses his enlightened wisdom to rescue and liberate all sentient beings, beings with blood and breath. Although beings without blood and breath, such as plants, are considered insentient, they do have natures, and they are born and grow within the Buddhas’ great bright light treasury.
A Bodhisattva is also defined as “an enlightened sentient being.” The Bodhisattva is the same as other living beings, except that he is enlightened. Being enlightened, he “does no evil and practices all good deeds.” He has no bad habits or faults. Having attained supreme wisdom, he is not confused anymore, so he does not act out of ignorance.
Ordinary living beings always bungle things up in their ignorance. They don’t have any real wisdom. When confronted with a problem, they don’t know how to handle it, because they are unenlightened. Those of the Two Vehicles are self-enlightened–they have come to understanding and are no longer confused. However, they have not tried to teach other people the method by which they themselves became enlightened. Bodhisattvas are self-enlightened, and they also share their enlightened wisdom with other living beings, teaching those beings to become enlightened through the method they themselves used. Bodhisattvas enlighten themselves and also enlighten others, but their enlightenment is not complete. A Buddha is one who has enlightened himself, enlightened others, and perfected his enlightened practice. Since he is perfect in the three enlightenments and replete with the myriad virtues he is called a Buddha.