What does open collector mean?

Question

Microcontrollers

I deal with input/output ports, the article
mcucpu.ru/index.php/stm32/82-stm32gpio
helped me, I perfectly understand how to program a specific mode, but the question is what each mode is?

• 
  00 – analog input.
  01 - input in the third state. (Set after reset).
  10 - pull-up input
  11 - reserved for future applications.
  

An analog input is an input to which a signal with a different voltage will be applied, for example, for digitizing to an ADC?
The input in the third state is a high impedance state - i.e. a wild resistance output?
An input with a pull-up resistor is an input that will have some kind of logic level, right? but which 1 or 0?
Reserved for future applications - I don’t really understand here, but apparently if it’s not worth using it at all, and why?
let's go further...

• 
  00 - digital output
  01 - open drain
  digital output 10 - digital output connected to dedicated units
  11 - digital output connected to dedicated open drain units
  

Digital output - will a set of zeros and ones corresponding to some letter be broadcast from the leg?
Open drain digital output - what does it mean?
Digital output connected to specialized blocks - what is this block? or as in the case of reserved for future uses?
A digital output connected to specialized open drain units - in general, the fantasy is over.
Please correct my answers. In order to take data from the thermistor, which mode is suitable? which one to flash the LED? Thank you!

Answer 1

https://ru.m.wikipedia.org/wiki/%D0%A2%D1%80%D0%B0...
- open collector (stock)
https://ru.m.wikipedia.org/wiki/% D0%92%D1%8B%D1%81...
- high-impedance state
easyelectronics.ru/avr-uchebnyj-kurs-ustrojstvo-i-...
- read about the purpose of pull-up resistors and in general I highly recommend this site for learning the basics.
To connect a thermistor, you need to assemble a voltage divider on a thermistor and a resistor of known value and measure the voltage output by this divider using an input operating in analog mode. The data will go to the built-in ADC of the controller.
To use an LED, you can take an open-drain output and connect the LED through a current-limiting resistor. Anode to the positive pole of the power source, cathode - through a resistor to the output of the microcontroller. Set the output to 0 - the LED will light up, 1 - it will turn off.