Awrah is the covering of your intimate parts of the body. This applies to both Men and Women and should be considered in a Muslims day to day life. Covering your Awrah is a prerequisite of Salah and can also change depending on your circumstances.
Mahram
A Mahram is an unmarriageable person with whom marriage is totally unlawful according to Islam. A short list is Siblings, Parents, Grandparents and Children. Depending on if your in the presence of a Non-Mahram or not, your Awrah can change.
Awrah for Women
For Prayer
Women should cover their whole body apart from their face, hands and feet. Without this, their daily prayers are invalid.
In front of a Non-Mahram
In front of women, navel to the knee.
In front of men, the whole body apart from their face, hands and feet.
In front of a Mahram
The entire body is permissible to be seen.
Awrah for Men
For Prayer
Men should cover their Navel (belly button) to their knee. Without this, their daily prayers are invalid.
In front of a Non-Mahram
In front of men, navel to the knee.
In front of women, navel to the knee.
In front of a Mahram
The entire body is permissible to be seen.