microchip - What's the difference between minimum feature size , transistor gate length and half pitch?

I've been looking into the limits that silicon based transistors. During this I've come across several terms describing the small size of a transistor, minimum feature size and transistor gate length are the most common, they seem to be used interchangeably. Another term used is half-pitch, half of the distance between two identical components. So what is the exact difference between the three terms, and which one is the most descriptive of the size of a transistor?