pronoun
your (informal singular)
A1
Dein is the informal singular German possessive determiner meaning “your” (for du). It modifies nouns and must be declined for gender, number and case (dein, deine, deinen, deines, etc.). Not used for formal Sie; use Ihr or Ihr(e) instead, commonly.
Examples
Ist das dein Buch?
Is that your book?
Der Lehrer kritisierte deinen Bericht, weil er viele Fehler enthielt.
The teacher criticized your report because it contained many mistakes.
Details
Mnemonics
Imagine pointing to someone's item and saying 'dein' (yours).
Sounds like English name 'Dein' — think 'your'.
Notes
'Dein' is the informal singular possessive pronoun; it declines to match gender and case of the noun.