What is a chasuble?
A chasuble is a Eucharistic vestment worn by priests. Essentially it is a special piece of clothing worn by a priest during a service at which s/he is celebrating Holy Communion.
What does a chasuble look like?
Basically, it looks like a fancy poncho. The color of the day (which depends on the liturgical season or the service being celebrated) tells the priest which color his/her chasuble should be. It will generally match the color of the altar-hangings.
What’s the history behind the chasuble?
The chasuble was created based off of what was essentially the overcoat of Greco-Roman times. Travelers would wear a long, flowy, poncho-like garment over their clothing to help keep themselves warm and protect themselves from the elements. So the origins of the chasuble are modest, but it has taken on a deeper meaning since its use as a Eucharistic vestment.