Refer to figure.
Note: Beware of the difference between lift force distribution and coefficient of lift distribution. Questions like this one have never been asked about before to our knowledge, so read the following explanation to understand the difference.

The planform of a wing is a fancy way of saying the shape of the wing when looked on from above. Wings can be made in many different planforms, which all have different properties, ranging from their spanwise lift distributions to their stall characteristics, transonic flight characteristics, ease of construction, etc.

Spanwise lift distribution is exactly as it sounds. It refers to the lift produced by each point on the wing, running laterally from the root to the tip. The simplest wing, a rectangular wing, has a spanwise lift distribution that is mostly flat, but drops off near the tip. This is not the most efficient planform for creating lift, as the high lift near to the tip (before the drop off) causes strong vortices, which cause induced drag.

An elliptical planform, however, is much more efficient when it comes to induced drag. An elliptical planform wing has much lower induced drag due to its shape, and the spanwise distribution of the lift force starts higher, and has a more gradual drop off towards the tip. This means that much smaller wingtip vortices are formed, as there is not much lift being created around the tip. (see bottom figure in annex

Now an elliptical wing is sometimes said to have a "flat" lift distribution, but that is referring to the coefficient of lift. The coefficient of lift of an elliptical wing stays almost constant along the whole span of the wing (top figure in annex), but because the actual chord line of the wing becomes gradually shorter towards the tip, the lift force decreases (as per the lift equation, where chord length directly influences wing area [S]). There are a few more complex reasons why this is so good for reducing induced drag, but we are not going to go into them. We are frankly surprised that the examiner has gone this far into the technicalities of wing planforms, as they have previously used greater oversimplifications.