Whats an offtank

Offtank is an outdated term used to describe a fighter. In classic MMORPGs, an off tank is the player who would soak damage while the tank healed up. In League, it basically means anyone who's tough and can take a few hits while still dealing damage.

Nobody calls them offtanks anymore though, now they are bruisers/fighters/juggernauts.

"Off-tank" is a character who has a mix of survivability and damage. AP/AD refers to whether you build Ability Power (AP) or Attack Damage (AD) as your damage source.

Off tank means "Offensive Tank".

Someone beefy enough to withstand hits by soaking damage and still not get bent over, but be able to build damage items [Like Trinity Force/Liandry's Torment] or damage/tank hybrid items [Rod of Ages/Abyssal Scepter & Banner of Command/Sunfire Cape tied with other damage items etc].

Examples of this would be:

• Garen
• Darius
• Shyvana
• Mundo
• Amumu
• Sejuani
• Nasus
• Renekton

Tanks are usually refered to being actual "pure tanks" because they synergize better just building straight defensive items with little or lack of being able to get damage out of offensive items and they also have to rely on their crowd control to make others focus them such as:

• Rammus
• Malphite
• Braum
• Leona
• Thresh
• Taric
• Shen
• Alistar
• Nautilus

Fighters can be referred to as Off tanks. Subsets of Fighters are Bruisers and Juggernauts, usually being a bruiser referring to champions to deal their damage in bursts as opposed to damage per second (DPS)

A bruiser basically

1 or 2 damage items and the rest tank items

In MOBAs, it generally tends to be that where the Tank is Tanky to protect others, an Off Tank is Tanky to defend themselves.

Think Volibear or Vi. Both can take hits, but not nearly as much as Naut or Leona.

Offtank refers to a tanky champion that tends to build 1 to 2 damage items at the start of the game before transitioning into a full tank build.

For example a renekton/darius who build ravenous hydra and black cleaver before building all tank items is an off tank because they are not nearly as tanky as a rammus/mundo who built only tank items, but they are much tankier than squishies.
Most tank supports are offtanks because they have less gold income and have to build sighstone so they usually dont' get super tanky quickly (alistar is the exception because his ult makes him very tanky).

Basically you want to have at least one dedicated tank or two off tanks in your team composition instead of all squishies.