static - HTML elements are positioned static by default. A static positioned element is always positioned according to the normal flow of the page. Static positioned elements are not affected by the top, bottom, left, and right properties.
fixed - the position is relative to browser window, it will not move ever the window scrolled. The content of a relatively positioned elements can be moved and overlap other elements, but the reserved space for the element is still preserved in the normal flow.
relative - A relative positioned element is positioned relative to its normal position
absolute - An absolute position element is positioned relative to the first parent element that has a position other than static. If no such element is found, the containing block is <html>. Absolutely positioned elements are removed from the normal flow. The document and other elements behave like the absolutely positioned element does not exist. Absolutely positioned elements can overlap other elements.