All HTML elements can be considered as boxes. In CSS, the term "box model" is used when talking about design and layout.
The CSS box model is essentially a box that wraps around every HTML element. It consists of: margins, borders, padding, and the actual content.
Padding is the space between the content and the border, whereas margin is the space outside the border.
An HTML elements height and width are determined by the user defined values for 'height' and 'width'. If you don't set the height yourself, the content of your division determines the height.
Padding 25px50px sets the top and bottom padding to 25px and sets the right and left paddings to 50px.
A border adds to the physical dimensions of an element, where as an outline doesnt affect the dimensions of the actual element itself.