Maths - Loci

SuperXDE

Hello , and peace be upon you

I have been answering a couple of past papers ... however I do not understand what does Loci mean at all ... the questions concerning Loci , like in 0580_s09_qp_2.pdf , FIrst Variant ,
16 Using a straight edge and compasses only, draw the locus of all points inside the quadrilateral
ABCD which are equidistant from the lines AC and BD.
Show clearly all your construction arcs.

I am completely clueless concerning that part , so could anyone give me a hand in it?
Is bumping allowed? ¬¬"