Ghayb:

Literally means "the unseen". In Islam it refers to all those things that are unseen by man and at the same time believing in them is essential. Examples of the unseen are: hell, heaven, angels, etc. A Muslim has to believe that no one has the knowledge of the unseen except Allah.

Ghayr Mahram:

Refers to all those people with whom marriage is permissible. Based on this, it is also incumbent to observe purdah with all ghayr mahrams.

Ghusl:

Literally means "bath, wash". In Islam it refers to the washing of the entire body from head to toe without leaving a single place dry.