The rendered font often depends on the local font your system provides, therefore you often find a rule like below in the computed style for an element:
font-family: Menlo,Monaco,Lucida Console,Liberation Mono,DejaVu Sans Mono,Bitstream Vera Sans Mono,Courier New,monospace,serif
This means if your system has a font named Menlo, it will render the text with this font. Otherwise it will try Monaco and so on. For the last two fallback options the system is free to use any monospace font or if not present any serif font. At least one serif font should be present on any system.
A side effect is the rendering of a different font on a different system, meaning the font changes e.g. between Linux and Windows. With chrome you can show the actual rendered font in the tab "Elements" > "Computed". Below all computed styles you will see a separated section with the name "Rendered Fonts":
Note: If you want to force a desired font on all systems you normally embed a webfont. This could still lead to some problems e.g. because of IE security settings.
