Memory or Variables?

I am trying to tell what is a memory location and what is a variable.
I have been looking at example code and see numbers such as
V1000
V2054.1
B2020.4
K100
V400
C100
I am very confused?

Those look like Automation Direct addresses and constants. download the user manual from:
http://web5.automationdirect.com/static/manuals/d006userm/d006userm.html

V - word address - in octal
K - constant - BCD/Hex depending on how it is used -> not where it is stored
B,V yyyy.xx bit of word address.- first part of address in octal, (word address), second part in decimal (the bit (0-15))
C - internal bit address.
X - input bit address
Y - output bit address

Thank You very much