TM,
"rolling call". Because the time of first taxing to departing can vary, with a rolling call anyone inbound now has a better idea time wise of where they'll be by the time you are setting track instead of waiting for you dep call, which if a jet could mean they'll be anywhere up to 7 miles out. While it's a double edged sword on busy freqs could be the last chance for conflicting traffic who missed your taxi call.