A vow was a promise made, a commitment made under oath to another individual, to a larger entity, like a deity or organisation, or indeed to oneself.
Leela believed that one should not make a vow they cannot keep. According to the Fourth Doctor, some monks took a vow of silence. (AUDIO: The Darkness of Glass) Some oaths were made as blood pacts. (AUDIO: Requiem for the Rocket Men)
According to Sister Jatt, Catkind nuns inducted into the Sisters of Plenitude took a lifelong vow to heal and mend the sick. (TV: New Earth)
Vows, known as wedding vows, (TV: The Power of Three) were also involved in a formal wedding ceremony. Pete Tyler stumbled on his vows when he got married to Jacqueline Tyler. (TV: Father's Day)
After the Dummy Massacre on 26 March 2005, people vowed to boycott shops with dummies, but soon went back on their word, although the shops did remove the hands of the dummies, a glimmer of acknowledgement of the attack that had unfolded not long before. (PROSE: The Doctor Was Involved in the Dummy Massacre)
According to Leela, the Doctor taught her that "Oaths taken in ignorance mean nothing." The same applied to oaths made under duress, or when given no other choice. Furthermore, she held that it was one's moral obligation to break an oath which was an "oath of evil". (AUDIO: Requiem for the Rocket Men)
The First Doctor took the Hippocratic Oath during his two years as a medical student before instead specialising in science, but did not forget his oath. (AUDIO: Farewell, Great Macedon)