#198: About the Position Property | CSS-Tricks

static: the default
relative: allows you to nudge around with top/right/bottom/left, making z-index work, gives you a positioning context
absolute: top/right/bottom/left moves the element to that exact position, otherwise the same as relative
fixed: like absolute, but scrolling the page doesn’t move the element
sticky: like fixed, but it doesn’t become fixed until the page is scrolled past your set threshold
inherit: makes the position values whatever the parent’s position value is

The almanac has more detail.