To keep the discussion as simple as possible let's ignore the niceties of instrument error and pressure sensing error, so that the ASI shows Indicated Airspeed.
Let's also stick to ISA msl to eliminate density errors, so that the IAS = TAS.
Now imagine that we have an aeroplane that is fitted with an Airspeed Indicator (showing Indicated Airspeed), a TASmeter (showing TAS). And a GROUNDSPEEDmeter (showing groundspeed) We also have an anemometer on the gound showing the speed of the air flowing over the ground.
The aeroplane is standing still on the runway facing into a 20 knot headwind.
The Airspeed indicator and TASmeter will read 20 knots.
The GROUNDSPEEDmeter will read zero.
The anemometer on the ground will read 20 knots.
Note that because of the 20 knot headwind, our airspeed is 20 knots higher than our groundspeed.
Now we accelerate to 180 kts relative to the ground.
The GROUNDSPEEDmeter will read 180 knots because that is our speed relative to the ground.
The anemometer on the ground will still read 20 knots because the wind has not changed.
The Airspeed indicator and the TASmeter will read 200 knots because that is our speed relative to the air. (We have 180 knots groundpseed + 20 knots headwind = 200 knots airspeed).
The key to all of this is the fact that the Airspeed Indicator and the TAS meter are measuring speed relative to the air. But the GROUNDSPEEDmeter is measuring the speed of the aeroplane relative to the ground. And the ground-based anemometer are measuring speed of the air relative to the ground.