Read the dictionary definition of bob. All definitions for this word.
1. a short abrupt inclination (as of the head)
1. he gave me a short bob of acknowledgement
2. a short or shortened tail of certain animals
3. a small float usually made of cork; attached to a fishing line
4. a hanging weight, especially a metal ball on a string
5. a long racing sled (for 2 or more people) with a steering mechanism
6. a hair style for women and children; a short haircut all around
7. a former monetary unit in Great Britain
8. cut hair in the style of a bob
1. Bernice bobs her hair these days!
9. make a curtsy; usually done only by girls and women; as a sign of respect
1. She curtsied when she shook the Queen's hand
10. remove or shorten the tail of an animal
11. move up and down repeatedly
1. her rucksack bobbed gently on her back
12. ride a bobsled
1. The boys bobbed down the hill screaming with pleasure
See also:
Merriam-Webster definition of bob