Knots/Binding knots/Reef knot
The reef knot or square knot is a common and simple binding knot.
Tying a reef knot 
To tie a reef knot, tie a left-handed overhand knot and then a right-handed overhand knot or vice versa. (Two consecutive overhands of the same handedness will make a granny knot.) A common mnemonic for this procedure is "right over left, left over right", which is often appended with the rhyming suffix "... makes a knot both tidy and tight".
The working ends of the reef knot must be cis (that is, both at the top or both at the bottom); the other lines lead to the full rope. Otherwise, a thief knot results. (The "cis" and "trans" terms are derived from terminology used to describe geometric isomerism.)
Used to tie two ends of a single line together such that they will secure something that is unlikely to move much. It lies flat when tied with cloth, and has been used for bandages for millennia. With both ends tucked (slipped) it becomes a good way to tie shoelaces, whilst the non-slipped version is useful for shoelaces that are excessively short. It is also used decoratively and to tie the Obi (or belt) of a martial arts keikogi. Finally, it is quite handy for tying plastic garbage or trash bags, as the knot forms a handle when tied in two twisted "ears".
This knot's name originates from its use to "reef" sails (tie part down to decrease effective surface area), where its easy-spilling behavior was very handy. A sailor could collapse it with a pull of one hand; the sail's weight would make the collapsed knot come apart.
The reef knot is one of the key knots of macrame textiles.
The reef knot's ease of tying and visually appealing symmetry belie its weakness. It is popular as a general-purpose binding knot. In particular, it figures prominently in Scouting worldwide: each Scout is said to know the square knot, and it is pictured in the international membership badge.
The International Guild of Knot Tyers warns that this knot should never be used to bend two ropes together. A proper bend (such as the double fisherman's knot) should be used instead. Some knotting guides claim that misused reef knots cause more deaths and injuries than all other knots combined.
Related knots 
Thief knot 
The thief knot is an intentional mis-tie of the knot, where the open ends are on opposite sides. It is traditionally used as an inexpensive method of detecting if a sack was opened where the thief would retie a standard reef knot. However, it does not provide as much strength for binding ropes.
Granny knot 
The granny know is a mis-tie of the knot by tying both portions of the knot in the same direction. This knot can release suddenly and unpredictably, and should be avoided.
Greif knot 
The grief knot shares common properties of both the thief knot and the granny knot, and likewise it is a weak knot. It is more of a trick knot, as it is possible to "lock" to knot so that it won't slip; however, locking this knot does not guarantee as much strength as the normal reef knot.
- Cassidy 1985, The Klutz Book of Knots
- Ashley's Book of Knots ISBN 0-385-04025-3