I've been reviewing the basics lately, and realized i'm having a hard time understanding "true airspeed." This is what I do understand about airspeed:

Indicated Airspeed- The number read directly from your airspeed indicator

Calibrated airspeed- Indicated airspeed, corrected for instrument/position and installation errors

Groundspeed- The speed you are traveling over the ground, which involves using an E6B to factor in any head/tail/cross winds you may be encountering

So now my question is, how does the term true airspeed play into all that and what would be the easiest way of calculating it?