A gartel is a type of belt worn by Jewish men while praying. The word gartel is actually the Yiddish word for belt; thus the origins of the word are quite self-evident.
Typically the gartel is worn by Hasidic Orthodox Jews though being Orthodox is not a requirement for wearing the belt. The belt is also worn by non-Orthodox Jews, though on a much less frequent basis.
Gartel’s are simple rope belts that are created with multiple strings all wrapped together and frayed at the ends. There is no significance to the number of strings used and the number can vary from under 10 to over 50.
The reason for the gartel is that Jewish law stipulates that there must be a physical separation between the genitals and the heart during prayer. Jewish authorities have deemed in the past that a regular belt is insufficient for this purpose and thus a gartel must be used to fulfill the separation requirement for prayer.