I am a Software Developer but I came from a non-CS background so maybe it is a wrong question to ask, but I do not get why logic gates/boolean logic behave the way they do.  

Why for example:

1 AND 1 = 1  // true AND true
1 OR 0 = 1   // true OR False
0 AND 1 = 0  // false AND true


And so on..
Is it a conditional definition for example, like it is like that by definition?
Or there is a logical/intuitive explanation for these results?

I have searched google, also looked at the Wiki page of logic gates for an explanation of 'why' but I can only find 'how'.
I would appreciate any answer or resources.

As stated by user120366, 16 possible 2-input logic gates exist, I've tabulated them for you here:

A|B||0|1|2|3|4|5|6|7|8|9|a|b|c|d|e|f
-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
0|0||0|0|0|0|0|0|0|0|1|1|1|1|1|1|1|1
0|1||0|0|0|0|1|1|1|1|0|0|0|0|1|1|1|1
1|0||0|0|1|1|0|0|1|1|0|0|1|1|0|0|1|1
1|1||0|1|0|1|0|1|0|1|0|1|0|1|0|1|0|1


A and B are the inputs, 0 through f are the possible permutations of outputs.

These gates have been named:

0 = FALSE 
1 = AND
2 = A NIMPLY B (A AND NOT B)
3 = A
4 = B NIMPLY A (B AND NOT A)
5 = B
6 = XOR
7 = OR
8 = NOR
9 = XNOR
a = NOT B
b = B IMPLY A (A OR NOT B)
c = NOT A
d = A IMPLY B (B OR NOT A)
e = NAND
f = TRUE


6 of these (0,3,5,a,c,f) discard one or both inputs. The IMPLY and NIMPLY gates are rare, though they are certainly used in formal logic. AND, OR and XOR are easiest for humans to reason with, but for physical hardware, NOR and NAND are also used heavily, because they can be simpler to implement and make smaller circuits. The same probably holds for XNOR.

So, as stated earlier, it's not so much that we decided that the gates should behave this way, but that 16 possible gates can be defined, and we came up with descriptive names for them.
