The term stopper knot has three distinct meanings in the context of knotting and cordage.

At the end of a line

A stopper knot is tied at the end of a rope

Rope

A rope is a length of fibres, twisted or braided together to improve strength for pulling and connecting. It has tensile strength but is too flexible to provide compressive strength...

 to prevent the end from unraveling, slipping through another knot, or passing back through a hole, block

Block (sailing)

In sailing, a block is a single or multiple pulley. One or a number of sheaves are enclosed in an assembly between cheeks or chocks. In use a block is fixed to the end of a line, to a spar or to a surface...

, or belay/rappel device

Climbing equipment

A wide range of equipment is used during rock climbing. The most popular types of climbing equipment are briefly described in this article. The article on protecting a climb describes equipment commonly used to protect a climber against the consequences of a fall....

. Knots commonly used for this purpose are:

• Overhand knot
  Overhand knot
  The overhand knot is one of the most fundamental knots and forms the basis of many others including the simple noose, overhand loop, angler's loop, reef knot, fisherman's knot and water knot. The overhand knot is very secure, to the point of jamming badly. It should be used if the knot is...
  
  
• Double overhand knot
• Figure-of-eight knot
• Stevedore knot
• Ashley's stopper knot
  Ashley's stopper knot
  Ashley's stopper knot, also known as the Oysterman's stopper, is a knot developed by Clifford W. Ashley around 1910. It makes a well-balanced trefoil-faced stopper at the end of the rope, giving greater resistance to pulling through an opening than other common stoppers...
  
  

Around the standing part

When a stopper knot is tied outside another knot and around the standing part it can also be called a backup knot. Tying the end around the standing part helps prevent the knot from unraveling by not allowing the end to slide back into the knot. Examples of this usage are often seen in climbing

Climbing

Climbing is the activity of using one's hands and feet to ascend a steep object. It is done both for recreation and professionally, as part of activities such as maintenance of a structure, or military operations.Climbing activities include:* Bouldering: Ascending boulders or small...

, rope rescue

Rope rescue

Rope rescue is a subset of technical rescue that involves the use of static nylon kernmantle ropes, anchoring and belaying devices, friction rappel devices, various devices to utilize mechanical advantage for hauling systems, and other specialized equipment to reach victims and safely recover...

, and other safety-of-life situations. Common knots used for this purpose are:

• Overhand knot
  Overhand knot
  The overhand knot is one of the most fundamental knots and forms the basis of many others including the simple noose, overhand loop, angler's loop, reef knot, fisherman's knot and water knot. The overhand knot is very secure, to the point of jamming badly. It should be used if the knot is...
  
  
• Double overhand knot/strangle knot
  Strangle knot
  The strangle knot is a simple binding knot. Similar to the constrictor knot, it also features an overhand knot under a riding turn. The difference is that the ends emerge at the outside edges, rather than between the turns as for a constrictor. This knot is actually a rearranged double overhand...
  
  
• Double fisherman's knot
  Double fisherman's knot
  The double fisherman's knot or grapevine knot is a bend, or a knot used to join two lengths of rope. This knot and the triple fisherman's knot are the variations used most often in climbing, arboriculture, and search and rescue...
  
  

Nautical usage

In nautical settings, a stopper may refer to a length of rope that is belayed at one end with the other end attached to a tensioned line using a friction hitch

Friction hitch

A friction hitch is a kind of knot used to attach one rope to another in a way that is easily adjusted. These knots are commonly used in Single Rope Technique while climbing to ascend a hanging rope by alternately hanging on one friction hitch and sliding the other up...

 in order to slacken a portion of the tensioned line. For example if a sheet

Sheet (sailing)

In sailing, a sheet is a line used to control the movable corner of a sail.- Fore-and-aft rigs:Fore-and-aft rigs comprise the vast majority of sailing vessels in use today, including effectively all dinghies and yachts. The sheet on a fore-and-aft sail controls the angle of the sail to the wind,...

 becomes jammed on a winch

Winch

A winch is a mechanical device that is used to pull in or let out or otherwise adjust the "tension" of a rope or wire rope . In its simplest form it consists of a spool and attached hand crank. In larger forms, winches stand at the heart of machines as diverse as tow trucks, steam shovels and...

 while under sail, a "stopper" can be used to temporarily take the strain off the winch while the riding turn is cleared.

• Rolling hitch
  Rolling hitch
  The rolling hitch is a knot used to attach a rope to a rod, pole, or other rope. A simple friction hitch, it is used for lengthwise pull along an object rather than at right angles...
  
  
• Other similar friction hitches