Abilities

Abilities are unique skills that Heroes have access to on the Battlefield. They range from simple passive effects, to devastating explosions of energy, to complex, terrain changing feats. All Heroes have four or more abilities, three or more Basic Abilities and an Ultimate Ability, that they can assign rank points to every time they level up. Every rank in an ability makes it more powerful, sometimes increasing its Mana cost as well.

Abilities can consume Mana, and may also be placed on Cooldown when used. Abilities that are on Cooldown can not be used until their Cooldown timer is up, at which point they can be cast again. Abilities with low Cooldowns are sometimes referred to as "spammable" Abilities, because they can be used very frequently.

Upgrading Abilities
Every time a Hero levels up, they earn a rank point which they can use to upgrade any of their abilities, learn a new ability, or can be used to upgrade their Attribute Bonus. At the start of the game, Heroes know none of their abilities, but are given a free rank point to learn one. Abilities cannot be used and do not have any effect if they have not been learned. After an ability is learned, it can be upgraded three more times, for a total of four ranks. The exception is a Hero's Ultimate Ability, which can only be upgraded to rank 3.

Basic Abilities can be upgraded to a new rank once every 2 levels. This means that a Level 2 Hero cannot upgrade a learned ability to rank 2. The same requirement applies to Attribute Bonuses. Every 2 levels, a Hero increases his maximum ability rank by 1. Ultimate Abilities can only be upgraded every 5 levels, starting from Level 6. These abilities are usually more powerful than a Hero's Basic Abilities.

Upgrading abilities will make them more powerful, or capable of doing more powerful things. Sometimes, upgrading abilities will also increase their Mana cost. For example, each rank in Earthshaker's Fissure increases the damage it deals and the duration of its stun, but increases its Mana cost by 15/rank.

Ability Types
An ability's type refers to how that ability's effects are applied.

Active
Active abilities must be used in order to apply their effects. Active abilities can consume Mana, have Cooldowns, and usually have some method of targeting related to them. Most abilities are active abilities. An active ability's effects can vary a lot. They may cause damage, apply Stuns, or buff a Hero or his allies. Active abilities are indicated by a bevel around the icon, which makes them look like a button. They can be activated by pressing their associated hotkey, and double tapping the hotkey can cause them to activate immediately on the caster.
 * Examples of active abilities are Weaver's Sukuchi, Ursa's Overpower, and Necrolyte's Reaper's Scythe.

Passive
Passive abilities will apply their effects as long as they are learned. They can be applied on the Hero that uses it, as an aura around that Hero, or even globally. Passive abilities do not consume Mana and usually don't have Cooldowns. Most Heroes have at least one passive ability, though not all do.
 * Examples of passive abilities are Skeleton King's Vampiric Aura, Crystal Maiden's Arcane Aura, and Drow Ranger's Marksmanship.

Autocast
Autocast abilities are special abilities that can be toggled on or off, or manually cast. When toggled on, the ability will apply when it can. For example, Drow Ranger's Frost Arrows will be used whenever she attacks a target. When toggled off, they will not be used and will not consume Mana. These abilities can also be manually cast for greater precision, in which case they fire off a single time. If the ability is a Unique Attack Modifier, it will be treated as a spell when manually cast, as opposed to a physical attack. This means that the user can cancel the animation earlier without nullifying its effect, while also giving it some other unique properties. For more information, see Orb Walking.
 * Examples of autocast abilities are Morphling's Morph abilities, Huskar's Burning Spears, and Enchantress's Impetus.