With a big assumption that everything below holds true or at least be similar to F7 series description. I could be completely wrong! Please double check!
According to the stm32 F4 family datasheet register description, the "ClockDivision" stands for
This bit-field indicates the division ratio between the timer clock (CK_INT) frequency and the
dead-time and sampling clock (tDTS)used by the dead-time generators and the digital filters
11: Reserved, do not program this value
I could not find any specific documentation related to F7 series and I am not quite aware of dead-time generators usage but ETR stands for "External Trigger Input".
Beware TIM1 is a special Timer, the same description do not hold true for other general pupose timers(ex. TIM2 etc.)
Also, HAL API Documentation is particularly not useful as it is just an accumulation of all the HAL Library comments without any description. If you are still interested, this might be helpful for you.