あの is classified as a 'pre-noun adjectival' in Japanese. These are a special type of word that do not conjugate. This means that they will always appear in the same form.
あの comes from the same family of words as
あれ and
あそこ, and is used to identify a 'thing' that is away from both the listener, and the speaker. It is usually translated as 'that' (thing over there).
あの子（こ）は可愛（かわい）いね。
That person is cute, don't you think? (子（こ） is often used to refer to any person in an affectionate way, regardless of their age. Primarily women)
あの話（はなし）はウソ？
Is that thing you said a lie? (That story that we both know about)
As the name 'pre-noun adjectival' suggests, these words will always appear before a noun, and describe that noun in some way.