Number of hours
 

When I see info on "incidents", the number of hours flying is usually quoted, eg PF had 16,000 hours experience, 10,000 on type.
How is this measured? From "clocking in" at the airport for work until flight is over, hours "behind the joystick", hours actually in the air, or what?

Normally from push-back (or start of taxi) until engines shut-down.
Some operators only log from take-off until landing.
Others log from take-off to landing plus a fixed allowance for taxi; e.g. 10 minutes.

Brakes Off after all doors and hatches are closed - last times Brakes On before first door or hatch to open aka Brakes Off/On

In helicopters, it's from the time the blades start turning for the purpose of flight until the blades have stopped turning. You can still crash a helicopter on the ground while not moving

Yep, where I was ;) , UK civil airline, it was recorded (automatically and FWIW sent to base via ACARS datalink) as described above.

But as eckhard has pointed out various definitions are available, for example during during my time in the UK Military it was time of take-off to time of landing.

Paul Lupp:

Roughly speaking that's what is known as Duty time, which you do sometimes see referred to in reports...

US military is wheels off to wheels on, an examiner told me that when got his civil license he was credited with extra hours to reflect this.

In the USA, it's not unusual for airlines to allow a flight time "conversion" factor for applicants with only military experience. .3 hours per sortie comes to mind since, as others have said, military only logs T/O to touchdown. However, you're still doing pilot stuff during taxi in/out.

For the purposes of simplicity for the general public consider the airplane moving as being considered “time” be it experience in general or type specific.