Different kinds of data for every purpose...
Almost every programming language stores information differently according to what kind of information it is. The different kinds of information are called datatypes.
By learning HTML/CSS/Javascript, you will need to know the difference between boolean, hexidecimal, integer, floating point, character, string, and date datatypes. You will also have to learn about binary datatypes, because that is essentially how everything is broken down by computers at a fundamental level.
These are not all the kinds of datatypes out there, but these are shared among the most programming languages.
Datatype definitions

Boolean =
A boolean is either true or false and is used for logic.
Example: true 
Binary = A number expressed in base 2 as ones and zeroes.
Example: 00001111 
Hexadecimal = A number expressed in base 16 as 09 & af.
Example: #ff55ff 
Integer = A whole number without a decimal.
Example: 42 
Floating point = A decimal number.
Example: 3.16 
Character = A single letter, digit, space, or symbol.
Example: % 
String = A sequence of characters in a row.
Example: "Don't press the red button!" 
Date = Specifies a particular day of a year.
Example: 9/8/2015