Boolean Logic

&& - true if both operands are true
|| - true if at least one operand is true
xor - true if ONLY one operand is true
! - true if a single operand is false

Let's just assume that:

X is a TRUE statement
Y is a TRUE statement
Z is a FALSE statement

X && Y
This is asking for X and Y to both be true, since they are both true, this expression is TRUE

X || Z
This is asking for X or Z to be true. Again this is a TRUE expression

X xor Y
This is asking for X or Y but not both, to be true. Since they are both true, this expression is FALSE

!X
This is asking for X to be false. Since X is true, this expression is FALSE

!Z
This is asking for Z to be false. Since Z is false, this expression is TRUE

Boolean logic is used a lot in computer programing. Say your program is searching a database for a certain type of person. They can't be male, or over 65 or under 21. You might run the logic like this:

First run the data through !male (! = not, so this is not male)
Then run the data though Age>21 && Age<65 (&& means both must be true)

Sometimes it helps to think of boolean less as these specific comparisons and more as a True or False way of thinking of things. For example, with the same search... we could think like this:

Is the person male: False
Is the person over 21: True
Is the person under 65: True

True/False, Yes/No, On/Off, 0/1, these are very useful questions to ask a computer with it's binary mind!!