HDMI in-ports vs HDMI out-ports (possibly related to damaged monitorHDMI OUT to OUT)

Here is my question:

Why does the Denon A/V Receiver 1909 have a difference in labelling at the back ?

At the back there are 4 HDMI ports, all of same connector type, all female or male... no difference. These all appear to be female.

3 ports are labelled as "in"... for example tv/dvd/hdp.

1 port is laballed as "out/monitor".

I connected the PC's graphics card to A/V receiver HDMI out/monitor first.

I kinda had a bad feeling about this... just slightly...

But I thought:

1. Probably won't cause damage, never happened before in 25 years of computer equipment handling.

2. Graphics/Monitor kinda belong together.

However...

This is now connecting:

GT 520 HMDI graphics OUT with A/V receiver HDMI OUT.

So where is my question:

What happens when two HDMI OUTPUT ports are connected together ?! WTF ?!

How is this even possible ?!

Also why would there ever be a male and female connectors ?! I have seen this this is weird.

Isn't HDMI supposed to be Peer 2 Peer ?!?

So another really important question:

What is the difference between HDMI IN and HDMI OUT ?!?!?!?!?

Could connecting OUT to OUT cause DAMAGE ?!?!??!

What happens to the GT 520 ?! When it's connected like this ?!

Will it dump excessive voltage on the chasis ?!

What if chasis is not grounded ?!

Will this voltage end up into the DVI cable connected to monitor causing damage ?!?!?!?!?!?

GT 520 has 3 outputs, vga, dvi, hdmi.

dvi was connected to monitor
hdmi was connected to a/v receiver hdmi out briefly... then it didn't work switched it over to hdmi in on receiver...

To me it seems this out 2 out may have caused damaged. Or switching the cable over from the 3 different hdmi's in to experiment ?

Bye,
Skybuck.