Canon EOS 6D Mark II Instruction Manual page 501

Exposure
: Metering start
When you press the shutter button halfway, exposure metering is
performed. (AF is not performed.)
: AE lock/FE lock
When you press the button assigned to this function, you can lock the
exposure (AE lock) while the metering timer is active. Useful when you
want to set the focus and exposure separately.
For flash photography, pressing the button assigned to this function will
fire a preflash and retain the required flash output (FE lock).
: AE lock
When you press the button assigned to this function, you can lock the
exposure (AE lock) while the metering timer is active. Useful when you
want to set the focus and exposure separately.
: AE lock (while button pressed)
The exposure will be locked (AE lock) while you hold down the shutter
button.
: AE lock (hold)
When you press the button assigned to this function, you can lock the
exposure (AE lock). The AE lock will be maintained until you press the
button again. Useful when you want to set the focus and exposure
separately or take multiple shots at the same exposure setting.
8: Custom ControlsN
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