na-adjective, noun
weak point; unskillfulness; poor at
Describes a personal weakness or lack of skill in a particular area. Often used in the pattern 〜が不得手だ.
私は数学が不得手です。
I am poor at mathematics.
彼は人前で話すのが不得手だ。
He is not good at speaking in public.
下手 is a more common and casual word for 'unskillful', whereas 不得手 is slightly more formal and often used in written language.
Compound of 不 (fu, 'not') and 得手 (ete, 'strong point'), literally meaning 'not one's strong point'.