Linden Lab Official:What is the difference between PG and Mature land?

Private Region/Estate/Island owners can indicate their land to be either PG or Mature from the Region tab of the Region/Estate window, using the Maturity dropdown list. This option is not available to Region owners on the mainland.

The PG and Mature ratings mirror those used by many countries' movie and television industries to denote the age-appropriateness of behavior, language and creations within a given area of Second Life.

PG Areas are designated to be free from sexually explicit language or behavior, swearing and other forms of aggressive language, violent behavior and/or imagery, including horror. Gambling for Linden Dollars is also prohibited.

Children and young people up to age 17 are automatically restricted to Teen Second Life, a special PG area that separates them from the adult population of Second Life.

Adults age 18 and over may seek an experience free of Mature content and so, we also offer PG areas within the adult regions of Second Life.

Mature areas are limited to the adult-accessible areas of Second Life only, and do allow adult language and behavior.

So how do I know where to draw the line?

PG regions have frequently been described as an area where you're free to say and do things that you would feel comfortable doing in front of your grandmother, or a grade school class.

In Mature regions, Residents can be free to engage in more adult activity and language, though of course, explicit adult content must be contained behind "closed doors".

However, if you feel there's some ambiguity as to whether or not your activity or content is allowed in a PG region, it's likely best kept to a Mature region.