Yep this is one of those areas where it seems 'model speak' reigns supreme. When I was taught aerodynamics there were only three types of tabs (and all of Pimmnz's examples fit into these);

Trim Tabs;

Both fixed and adjustable, for trimming the neutral point of a control surface so the pilot didn't have to continually have to hold pressure on the controls, allows for more accurate and less tiring flying.

Never ever try to trim a model plane with these.

Balance (or Antibalance) Tabs

Makes the controls easier for the pilot to move, usefull on larger or faster aircraft (may also be adjustable for trim)

Antibalance tabs make the controls harder to move, this may be reguired where large controls have horn balances. As Rotaryphile says horn balances can be non linear and cause controls to overbalance at large displacements, antibalance tabs can fix this.

Balance tabs can be used on models with great success and allow the normal servos to drive larger and/or faster models.

Servo tabs

With these the pilot 'flys' the tab only. The tab then acts as a servo (not the rc kind) and flys the control surface for the pilot. As Pimmnz points out these normally have a spring connection to the surface so that at low control loads the pilot flys the control surface, as control loads increase the spring deflects allowing the tab to fly the control surface. The pilot only ever feels the spring loading. They may also be used for trim.

I never realised that these were being used in models but clearly they are.

I don't know where boost tabs come from, maybe it's the American name for Balance tabs or Servo tabs, maybe it's a term invented by aeromodellers. Passive boost tabs? I have no idea, did we just invent that term in this thread.

Iron Eagle you would be hard pressed to find a higher performance or heavier aircraft since the 30's or so that doesn't have tabs of some sort, Nearly every WW II aircraft has them. Even the light low perrformance aircraft will have at least a plain trim tab.

Dave H