Bond

A bond is an in-game item that allows a player to pay for selected account-related and out-of-game benefits such as membership, Runecoins and Treasure hunter keys with in-game resources.

Tradeable bonds may be traded to other players and sold on the Grand Exchange; however, when the transaction is complete, the bond will become untradeable. A bond is always bound to a player when it has not been redeemed or traded to another player. It is always kept on death, even when inside the wilderness.

Uses
When bought using real life currency, bonds are tradeable. Once traded to another player for an in-game sum of money or items they become untradeable. Bonds can be made tradeable again for a payment of 10% of their Grand Exchange value (i.e. 10% currently being coins).

At any time, whether tradeable or untradeable, bonds can be redeemed for one of the following:
 * 14 days of membership (Counts for oldschool as well, enabling F2P in oldschool)
 * 8 Treasure Hunter keys
 * 160 RuneCoins

Bonds can be used:
 * To trade with other players
 * By selling for in-game money
 * To buy RuneFest tickets (when tickets are eligible to be purchased during the year)
 * To donate towards charity via the Well of Goodwill when it is active (currently active, as of GameBlast February 21-22)
 * To buy Premier Club membership (when eligible to be purchased during the year)
 * To buy Top Trumps

Price per unit
The below prices are subject to change, depending on a bond's Grand Exchange value:

Charitable donations
Jagex donated approximately $4.70 per bond put into the Well of Goodwill, slightly less than the purchase price. A selection of charities benefited from the donations.

It can also be used as a form of donation to the Well of Good Will for Helping Disabled Children play Games during The Bonus Exp Weekend of February.

Controversy
A section of the RuneScape community found the introduction of bonds hypocritical and destructive to the integrity of the game, claiming that it was real world trading in the form of gold selling. This is due to the fact that the bonds can be bought with real-life money and sold for in-game gold.

Similar to certain responses to the Squeal of Fortune uproar, Mod Weath has this to say regarding buying gold through bonds:

"Buying the most expensive item in the game isn't going to give you an edge over other players though is it?"

Trivia

 * Despite being tradeable, bonds cannot be placed in the party chest at the Falador Party Room, stored in the treasure chest from Carnillean Rising or a beast of burden; they may also not be staked at the Duel Arena or in Conquest; they may not be fed to a Baby Troll.
 * When buying membership in the UK, two bonds costing £6, giving 28 days, are cheaper per day than buying a £7.50 30-day membership card, but more expensive than buying 30 days of membership directly for £4.95.
 * The outside rim of a bond appears to be 4 hands grabbing each other's wrist.