Absolute Xpath: It uses Complete path from the Root Element to the desire element.
Relative Xpath: You can simply start by referencing the element you want and go from there.
Relative Xpaths are always preferred as they are not the complete paths from the root element. (//html//body). Because in future, if any webelement is added/removed, then the absolute Xpath changes. So Always use Relative Xpaths in your Automation.
Below are Some Links which you can Refer for more Information on them.
- difference-between-absolute-path
- xpath-tutorial-for-selenium
- choosing-effective-xpath