derselbe meaning and definition in german

When preceded by a preposition that contracts with the definite article, the form selbe or selben is written apart: zur selben Zeit (“at the same time”).
Purists prescribe that derselbe should be used only when one refers to physically the same object, whereas der gleiche should be used when referring to an object of the same kind. For example:
Ich habe früher dasselbe Auto gefahren. – “I used to drive this very same car.”
Ich habe früher das gleiche Auto gefahren. – “I used to drive the same kind of car.”
However, this rule is an artificial prescription often ignored in standard usage, let alone colloquial German.