An expression meaning 'a certain kind of' or 'to some extent' used to indicate a particular quality or category (as in 'a sort of ~' or 'in a sense').
彼の態度はある種の勇気の表れだ。
His attitude is a display of a kind of courage.
これはある種の伝統で、地域ごとにやり方が違う。
This is a kind of tradition, and the way it's done differs by region.
ある種、彼の成功は必然だったとも言える。
In a way, one could say his success was inevitable.