Well these ratings represent Indian films rating given by Central certification board after assessment. Based on content of the film, films are rated as U, U/A, A and S.

When you start watching Indian movie, you would find this certificate first which will mention the specific rating allocated to movie.

The explanation for U and U/A are provided below with reference from Wikipedia.

• U (Unrestricted Public Exhibition)

Films with the U certification are fit for public exhibition, and are often family friendly. These films can contain universal themes like education, family, drama, romance, sci - fi, and action etc. Now, these films can also contain some mild violence, but it should not be prolonged. It may also contain very mild sexual scenes (without any traces of nudity or sexual detail).

• U/A (Parental Guidance for children below the age of 12 years)

Films with the UA certification can contain moderate adult themes, that are not strong in nature and can be watched by a child under parental guidance. These films can contain some strong violence, moderate sex (without any traces of nudity or sexual detail), frightening scenes and muted abusive and filthy language.

Additionally, V/U, V/UA  are used for video releases with U, UA and A carrying the same meaning as above.