Girths, which in western riding is referred to as a cinch, is used to maintain the saddle in position on your horse. The girth runs under chest of your horse and is attached to the saddle on either side via two or three leather straps referred to as billets.
Girths are found on English and Australia saddles, while Cinches are found on pack and western saddles, whereby the cinch is attached to the saddle by one wide, single leather strap on each side of the saddle. This strap is called a latigo. Whilst a girth is usually substantial enough to maintain the saddle in place, in some equine disciplines such as show jumping, polo, eventing and on steep and rough terrain trail rides additional pieces of equipment are used including cruppers, overgirths, surcingles and breastplates, whilst on pack saddles breeching is used.