A Turnover is generally defined as either a Fumble Lost, Interception thrown or a 'Turnover on Downs'. To be recorded as a Turnover however, it must occur on either an ordinary offensive play from scrimmage or a kick return (fumble).
Turnovers are NOT recorded when there is either a Fumble Lost or Interception thrown on a Two-point convert attempt. The primary reason for this is that no new series of downs takes place on the immediate next play despite the defence having temporary possession of the ball for the purposes of a return. Additionally, the next play is in most cases a kickoff anyway (for which possession is retained initially by the team that attempted the Two-point convert).
Turnover Ratio is defined as the difference between Team Turnovers (also known as Giveaways) and Opponent Turnovers (also known as Takeaways or Turnovers Forced). CFL Statistics will also measure the effect of Turnovers by counting the subsequent points scored after a Takeaway i.e. 'Points Off Turnovers'.