What is the significance of icons below the name of an app in play store?

PEGI stands for "Pan European Game Information" and is used to advise on the suitability of the app for certain age ratings. There are 5 age categories (sourced from wikipedia):

• 3: Suitable for ages 3 and older. May contain very mild violence in an appropriate context for younger children, but neither bad language
  nor frightening content is allowed.


• 7: Suitable for ages 7 and older. May contain mild or unrealistic violence (e.g. violence in a cartoon context), or elements that can be
  frightening to younger children.


• 12: Suitable for ages 12 and older. May contain violence in either a fantasy context or a sporting action, profanity, mild sexual
  references or innuendo, or gambling.


• 16: Suitable for ages 16 and older. May contain explicit or realistic-looking violence, strong language, sexual references or
  content, gambling, or encouragement of drug use.


• 18: Unsuitable for persons under 18. May contain extreme or graphic violence, including "violence towards defenceless people" and
  "multiple, motiveless killing", strong language, strong sexual
  content, gambling, drug glamorisation, or discrimination.

The icon shown in the Play Store will indicate which category the app has been rated suitable for.

Other areas of the world have similar rating systems such as ESRB and ACB