The absolute minimum speed on approach is Vls (lowest selectable speed), which is the top of the amber strip on the speed scale. It is the absolute minimum speed you can fly for any given configuartion. It a multiple of the stall speed of the aircraft in the current configuration, the multiple varies according to whether the flaps are extended or not, and if they are, which setting exists.
When a landing flap configuration is selected (i.e. either full flap or flap 3), the Vls is equal to 1.23 Vs (stall speed). In this case, Vls = Vref.
The target fly speed on approach is the magenta arrow on the speed scale, which represents Vapp. Vapp = Vls + (5 knots or 1/3 of the headwind component, whichever value is greater). If 1/3 of the headwind component > 5 knots, you add the actual value up to a maximum of 15 knots.
An A320 at 64 tonnes (MLW = 66t): Vref, flap full, is 134 knots and Vref, flap 3, is 139 knots, so the normal approach speed is 139 knots and 143 knots respectively.
F speed: Minimum speed at which the flaps may be retracted at takeoff.
In approach, used as a target speed when the aircraft is in CONF 2 or CONF 3.
Represented by "F" on the PFD speed scale. Equal to about 1.18 VS to 1.22 VS of CONF 1 + F.