What is identation error?

Answer 1

that only occur in python to my knowledge, and that error only occur when you do not format your code properly, python consider white space as syntax too

Answer 2

It's about spaces and tabs.It mostly happens in python and languages like it.
In python you have to write main codes without spaces in the beginning of line and you use tabs for making function. So this two code bellow will occur indentation error:
print('hi')
print("what's up?")
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def say_hi():
print('hi')