rubyの文字列+コロン(Stack Overflowからパクリ)

What is the difference between:
1) abc:
2) :xyz
3) abc::xyz
4) abc: :xyz
5) abc: xyz
6) :abc => xyz
Please post if I've missed any of them.
1)  abc:  it can't exist independently
2)  :xyz  it is a symbol

:xyz.class
 => Symbol

3)  abc::xyz  it represents namespace
Example code:

module ABC
    class Xyz
       def initialize
         @size = 400
       end
    end
end

x = ABC::Xyz.new

4)  abc: :xyz

hash = {abc: :xyz} #hash key and value all are symbol. 

5)  abc: xyz

xyz = "just a test"
hash = {abc: xyz} #hash key is symbol, value is string. 

6)  :abc => xyz

xyz = "just a test"
hash = {:abc => xyz} # same with (5)， just another representation

7) ternary operator  :

abc = 1
xyz = 2
result = abc > xyz ? abc : xyz
=> result = 2