What do "root," "flash," and "ROM" mean?
Looking around the site will give you lots of answers.

Rooting:


What does &quot;to root a phone&quot; mean?
How do I root my Android device?


ROMs and Flashing:


What is the meaning of &quot;flashing a custom ROM&quot;?
Does flashing a custom ROM require root access?
Does rooting require a custom ROM?