What does ‘b’ represent in figure?

Among newly synthesized two strands , one strand is continuous and another strand is discontinuous. Continuous strand is leading strand and discontinuous strand is lagging strand. Leading strand is synthesizing on template of 3'--5' polarity and lagging strand is synthesizing on template of 5'--3' polarity. We observe that there is the synthesis of okazaki fragments w.r.t. the strand ‘b’. Hence, strand b is the lagging template strand having 5' to 3' polarity.