Basics of GvG, part 1

Spike: This is where your entire build centers around dealing a very large amount of damage in a short amount of time, but not much else. These builds are the most lethal, but they're also easier to take apart if you know what to do. Generally, they can't adapt as well to a split situation since the offense can't really be broken up (usually at least 5 members of the team are devoted entirely to offense). Common types of spikes include: ranger, air, blood, adrenal, and FoC (Feast of Corruption).

Defensive: Defensive builds will sacrifice offense in order to play defensively and keep the team (and NPCs) alive through Victory or Death (VoD). There will be very few deaths during these matches, both because the defensive team keeps themselves protected and because they don't put out as much damage as they need to in order to hurt most teams.

Balanced: Balanced is a team that is focused on a balance (hence the name) of offense, defense, and utility skills that allow a build to adapt to a wide variety of situations. These are the most capable of splitting up the group to accomplish differing objectives. Balanced builds are the most common build type and most accepted among players.

Gank: Gank teams are basically a team designed specifically to split, where one (usually defensive) team goes to the flag stand defends that, while the other team goes directly to the enemy base and starts taking out NPCs. They're mostly built to wait for VoD so they have an advantage when all the NPCs head to the center. They also make it harder for a team to fall back and be under the protection of their base NPCs should something go wrong out in the field. Assassins have mostly found their niche in GvG builds as the center of gank squads (or even as solo gankers).

Pressure: Generally a build that is designed to constantly put out constant damage and energy denial. Whirling Axe and Cleave are warrior skills suited to pressure. The main idea is to wear the other team down; deplete the monks' energy so they can't heal the team anymore and people just start dying while the team collapses. These types of teams also have a lot of energy drain utility skills, such as Debilitating Shot and Energy Surge/Burn. They also feature large amounts of health degeneration in the forms of conditions (bleeding, poison, disease) and hexes (Conjure Phantasm, Life Siphon, etc.)

Gimmick: Gimmick builds are also referred to as Flavor of the Month builds. They rely on using one or two skill combinations that, when put together, are considered cheap by most of the PvP community. This does not mean they aren't effective or without merit, they're just shunned as requiring little skill and builds that can't stand against a better, more balanced team. IWAY is considered a gimmick build (although it should be noted that IWAY is also a pressure build) and is the most common type of Gimick you'll see (ranger spike has also been considered a gimmick build).