This classification is based on the endings that appear after the stem of an adjective. Some adjectives (the overwhelming majority) have Nominative and Accusative endings that consist of two letters (как-ћй, как-ђя, как-ће, как-џю 'which, what'); these are called ordinary adjectives. A complete set of endings for them is shown in chart for basic case endings.
Other adjectives (very few in number) have Nominative and Accusative endings that consist of no more than one letter (вђш-#, вђш-а, вђш-е, вђш-у 'your'); these are special adjectives. A complete set of their forms is shown in the chart for special adjectives.
Ordinary adjectives are entirely regular. When you learn an ordinary adjective all you have to memorize is one form, the dictionary form (Nominative Singular masculine), and if you know the general rules of spelling you can make up all the other inflected forms of the adjective without error.
Special adjectives, on the other hand, have various peculiarities (stress shifts, irregular stem changes, irregular endings), and they should be learned by heart. Special adjectives have special meanings (possessives like 'my, your'... and demonstratives like 'this, that'...) and it is therefore easy to remember which adjectives are special and which are not.
In sum, special adjectives are special in three senses:
  1. they have five distinctive single-letter endings
  2. they have various irregularities
  3. they have distinctive meanings
Here are a few examples:
  Ordinary Special
Nom.Sg. masc. какћй рџсский трџдный мћй вђш чљй
Nom.Sg. neut. какће рџсское трџдное моё вђше чьё
Nom.Sg. fem. какђя рџсская трџдная мої вђша чьї
Acc.Sg. fem. какџю рџсскую трџдную моє вђшу чьє