The phrase "overall turnout" refers to the total number or percentage of people who participate or show up for an event, activity, or a voting process as a whole. It gives a general overview of the overall level of participation. Full definition
[3] Overall turnout in the election was 38 %. (en.wikipedia.org)
[4] Overall turnout in the election was 38.24 %, in increase from the 31.33 % in 2003, and put down to the European elections being held at the same time as the council election. (en.wikipedia.org)
[6] Overall turnout at the election was 51.5 %, an increase from 37 % in 1999. (en.wikipedia.org)