This is the 10773rd most frequent Turkish word.
defterime
"Defterime" means "to my notebook" in English.
The word 'defterime' in this sentence indicates possession ('my notebook') and specifies the object of the verb 'yazdım' ('wrote').
Defterime güzel bir şiir yazdım.
I wrote a beautiful poem in my notebook.
Here, 'defterime' again indicates possession and establishes the notebook as the place where the action of noting goals occurred.
Defterime bu yılki hedeflerimi not aldım.
I noted down my goals for this year in my notebook.
The term 'defterime' specifies the intended usage context, showing the purpose of purchasing the pen.