Frame is an option for two-dimensional graphics functions which specifies whether a frame should be drawn around the plot.
Frame -> True by default draws a frame with tick marks. If Ticks -> Automatic, setting Frame -> True suppresses tick marks on axes.
See The Mathematica Book: Section 1.9.3, Section 2.9.1, Section 2.9.5 and Section 2.9.5.
See also: Boxed.