What is the difference between Thread.Sleep() and Selenium.setSpeed()?

Selenium.setSpeed:
1. takes a single argument in string format
ex: selenium.setSpeed(“2000″) – will wait for 2 seconds
2. Runs each command in after setSpeed delay by the number of milliseconds mentioned in setSpeed.

Thread.sleep:
1. takes a single argument in integer format
ex: thread.sleep(2000) – will wait for 2 seconds
2. Waits for only once at the command given at sleep.