Hearthstone has many card effects that are common enough that they get their own keyword - a word or two that immediately tells you how the card works. Let's take a look at the Outcast keyword.
Enemies must attack this minion.
Taunt is one of the most ubiquitous keywords in the game. Minions with Taunt will force enemies to attack it before it can attack other minions or the enemy hero. If a player controls multiple Taunt minions, the other player can choose which of the Taunt minions to attack, although they must all be eliminated before other targets can be attacked.
Taunt only works on attacks, meaning that effects, spells, or Hero Powers will still be able to target anything regardless of any presence of Taunt minions. A minion cannot have Stealth and Taunt active at the same time. If a minion has both Stealth and Taunt, the Taunt will not take effect until it loses Stealth. This also applies to Immune.
Keywords that Work Great with Taunt
Most keywords work great with Taunt. Divine Shield will increase a Taunt minion's survivability, and in turn, take more hits and protect your other characters better. Lifesteal can provide healing as minions will be forced to attack into it. Any artificial Deathrattle effects are also strong with Taunt as it will effectively force your opponent to activate it.
Although Rush and Charge have no direct synergy with Taunt, it will allow you to deal some damage and create a wall at the same time.
Playing Against Taunt in Hearthstone
As specified before, Taunt will not prevent the other player from targeting other characters with abilities, spells or Hero Powers. This means that if your opponent is protecting a high-priority target with a Taunt minion, you can still target it with removal without needing to remove the Taunt minion. This also means that you can kill your opponent with spells through Taunt minion.
Taunt can be removed by Silence effects, and The Black Knight will destroy any enemy minion with Taunt. Kayn Sunfury also allows you to bypass Taunt effects, although they will be active again if Kayn dies.
Example Hearthstone Taunt Cards
Sen'jin Shieldmasta is a Basic Taunt minion that simply has the ability and nothing more. Although it has been shuffle out of play due to powercreep, it's still a strong card for new players.
Sunfury Protector is a card that gives minions Taunt, specifically ones that are adjacent to it when you play it. The card is often used in Handlock to give Taunt to Ancient Watcher or any of your Giants.
Eye of the Storm is a spell that summons Taunt minions, specifically summoning three 5/6 Elementals with Taunt.
Fire Plume's Heart is a Quest in which you play 7 Taunt minions (meaning that they can't be cheated out), and in which case, you will be rewarded with Sulfuras.