Fixed odds betting is when you take a betting price. If you bet on a selection at, say, 5/1 odds then you have taken a betting price. That is fixed odds betting.
Tote or Pool betting is not fixed odds betting: you don’t know the price you will get when you back a selection with Tote betting because the dividend is not worked out until the event starts.
With fixed odds betting you have taken a specific price or betting odds when you struck the bet. So, if you take a price on football team or a horse (including Early Prices or Board Prices) then that is fixed odds betting because you have taken fixed betting odds.
In the case of horse racing if you take a fixed odds price on the day of the race there may be a Rule 4 deduction in the event of a horse subsequently becoming a non-runner.