Usman, which can also be spelled as Uthman, Osman, Othman, Uthmaan, and others, is an ancient Arabic name for boys that means "snake". It was common practice among Arabs to name their children after animals and insects, thinking that this would prevent their children from being harmed by envious people. It is a popular name among Muslims due to the fact that it as the name of a close companion of the Prophet, peace and blessings of Allah upon him, who became the third righteous caliph, Uthman ibn Affan.
When the Prophet thought that a person's name was a bad name, he would change their name. Therefore even though the meaning of "snake" doesn't sound all that great, the fact that Prophet didn't change the name shows that it is an acceptable name for Muslims.