What makes the prohibition of ḥameṣ so unique is that, unlike any other forbidden foods, it includes the ban of its possession. There are three miṣvot in the Tora related to this prohibition: bal year-e (your ḥameṣ shall not be seen); bal-yimaṣe (ḥameṣ shall not be found in your possessions), which our Rabbis explain as one single prohibition: owning ḥameṣ during Pesaḥ. We also have a thirdmiṣva called tashbitu (you shall end the possession of ḥameṣ, before Pesaḥ begins). In sum, there are two identical prohibitions (an exceptional case!) and one positive commandment, virtually for the same issue: owning ḥameṣ during Pesaḥ.
Strictly speaking, (and following Maimonides opinion) these three miṣvot would be fulfilled at once by the 'bitul', i.e., a verbal declaration by which we renounce to the ownership of any ḥameṣthat belong to us, regardless of where that ḥameṣ is located.
But the Rabbis explained that there might be some practical complications with just declaring our ḥameṣ ownerless, while keeping at home. First, we might declare that we do not own anymore our ḥameṣ, but, if we posses something valuable, will we really mean wholeheartedly that we renounce to its possession? Second, ḥameṣ is the most common food (bread, etc.), so even if we declare it ownerless but we keep edible ḥameṣ at home, we might eat it accidentally...
This is why our rabbis instructed us to actually dispose of ourḥameṣ before Pesaḥ begins.
There are four steps, then, that we should take to fulfill these three Biblical commandments according to our ḥakhamim:
(1) We should clean our houses, cars, offices and other properties before Pesaḥ to identify and remove all ḥameṣ from our properties.
(2) We have to run a final search of all our properties to make sure that we have removed everything ḥameṣ from them (bediqatḥameṣ).
(3) We have to physically dispose or get rid of any ḥameṣ found in our properties before and during the Bediqa (be'ur ḥameṣ).
(4) Then, we have to declare that whatever ḥameṣ we may still own anywhere, which was not detected and eliminated by us, does not belong to us anymore, and from now on it is considered ownerless (hefqer) as the dust of the earth (bitul ḥameṣ).
We will explain each one of these steps, B'H, in the coming HOTD.