The line is just a bond. You draw it like that when you are unsure or don't care where exactly it should connect to the benzene ring.
– Ivan NeretinJun 14 '19 at 13:35
1
Just a clarification to @IvanNeretin's comment: It's when it may be of any configuration -- ortho-, meta- or para-substituted.
– Eashaan GodboleJun 14 '19 at 15:13