The CSS box model consists of the invisible spaces that are separated by the padding, margins, and borders, with the content in the center. This box "wraps" around all HTML elements.
The difference between margin and padding is that margin deals with the spacing outside the borders while padding deals with the spacing inside the borders, right next to the content.
The height and width of an HTML element is determined by either a percantage sign or in pixels, cm, pt, etc. Percantages will take the width of the page with margins taken into consideration, while any numbered legnths or widths that use some form of measurement will be fixed
This CSS property would mean that the spacing inside the borders, between the content and the border, would be 25 pixels on the right and left and 50 pixels on the top and bottom, all in relation to the borders and the content.
The difference between a border and an outline is that borders have to do with the html elements, all in relation to the margins, content, and padding. On the other hand, an outline actually deals with only the html tag itself, so is separate from the border in what it is related to. So, the outline is actually outside the borders.