In regards to digital cameras and ISO setting:

What does ISO mean?

What does ISO do or effect?

Is ISO of 100/200/400/800 same between cameras?

How should ISO be set or ISO value chosen?

Let the ISO discussion begin...

See Post #8 for articles and answers

The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera. The component within your camera that can change sensitivity is called “image sensor” or simply “sensor”.

Lower ISO means more light and less grain in the image (sensitivity). On bright days, you may want to take the ISO up, or you may need an ND filter which more or less acts as an Aperture adjustment which is not on the Mavics. Aperture is fixed.  On darker skies of early morning or sunset, you want the ISO lower in order to capture more light on the sensor, and less grain (noise) in the video or image.

ISO is just an acronym for International Standards Organization.

This chart is commonly shared, and visually helps new photog's to see the "exposure" relationship of ISO, SS, and Aperture

this too:

Ultimately on digital it refers to the gain of the sensor (as opposed to sensitivity of grain on film).
The higher the ISO the more sensitive the camera is to light but the more noise you get on the image.
The Mavic range is generally awful at anything other than ISO100 with 200 or more being unusable for most tasks whereas a good DSLR can go into the mid 10s of thousands range and look the same.

For video, you want to follow the 180 rule. That just means set Shutter Speed to 2x your chosen frame rate.

In reference to original posted questions, something to consider - Jpeg and RAW.

This may help those old-timers coming from Film days...
Film (aka Kodachrome) ISO ≠ ISO sensor (aka electronic / digital)

I admit, had someone ask me opening questions, I would have respond similar to what most have posted.  

That was until I read following article on ISO and digital cameras:  You probably don't know what ISO means – and that's a problem
Which lead to another article involving sensors and ISO: Sense and Sensitivity


For enlightement, and peaking interest in above articles: Brief attempt at answering opening questions:

What does ISO mean?
ISO is a standard, with five defintions.  Of which ''two definitions of ISO that are actually used by camera manufacturers  (and are reported by their cameras) are based on the brightness of  cameras' JPEG output.''  What about RAW?
One of two ''defines ISO as the camera behaviour that renders middle grey at the correct brightness''.  Again, where's RAW...
Other of two ''aim to achieve whatever the manufacturer considers to be 'correct' exposure.''  Method that may be used for RAW, but not necessarily.

What does ISO do or effect?
Sensor's sensitivity is not changed by changes to ISO setting.  A common misconception is that a change to ISO setting, changes the sensor's sensitivty to light.
The answer depends upon digital camera's maker.  Mostly, a camera sensor's analog output is sent to amplifier which changes amplitude, with output of amp going on to be converted from analog to digital signal.
''However, it is also possible to mathematically manipulate the data once  it has been digitised - many 'extended ISO' settings and some  intermediate ISO values between full stops (e.g. 250 and 320) do just  that.''
Answer also depends upon image format that camera is set to store images to, Jpeg or RAW.
''ISO standard doesn't specify that amplification needs to be used, nor  does it specify what happens in the Raw file.  All it does is relate  initial exposure to output JPEG lightness,''
Digging deeper: ''Olympus E-620, we noticed that the dynamic range was much lower at ISO 100 than at 200 and above.''  Going by common understanding of ISO, one would expect opposite.
Leading to question: ''is the Olympus underexposing ISO 100 to produce its ISO 200 or is it overexposing ISO 200 to give an ISO 100 setting''

Is ISO of 100/200/400/800 same between cameras?
Sort of, kind of, maybe.  Camera makers use their own methods, and ISO brightness can vary between camera maker's different model-lines.  Given two common defintions to choose from, manufactures have their own defintion of correct birghtnes or exposure.  And a camera maker may impelment digital processing (after amplification & conversion to digital).
''ISO definition used when you take photographs is based on the brightness  of the resulting JPEGs, not on any inherent property of the sensor.''  Different sensor maker, different sensors, different results - standardized; not necessarily what gives best resulting image.  Lastly throw in aforementioned E-620 ISO 100 vs. 200.

How should ISO be set or ISO value chosen?
''Cameras light meters (even 'highlight' metering modes) are based on JPEG  output and the majority of them, per the ISO standard, are designed to  'correctly' expose a middle grey.''  Thus, in general leaving RAW out of picture (pardon the pun).
''The best results are achieved by giving as much exposure as possible without clipping the brightest tones you care about:  a process called ‘exposing to the right.’ This maximizes the amount of  light, and hence signal which, in turn, optimizes the signal-to-noise  ratio (essentially ‘noisiness’).''

DJI Wanda Posted at 2018-8-8 08:36
The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera. The component within your camera that can change sensitivity is called “image sensor” or simply “sensor”.

From professional article - You probably don't know what ISO means – and that's a problem
''Despite what you may have heard or read, changing the ISO of your camera does not change its sensitivity.''

''ISO changes the lightness of the final image but it doesn’t change the fundamental sensitivity of your sensor.''