Question: what does odds 2/7 mean?
Answer: 2-7 (or 7-2 ON) means you get 2 units for every 7 staked. Don't forget, though, that your original bet is still returned, so you still win overall. Eg a £100 bet on a horse at 1-2 pays out £150 (1 / 2 x 100 + 100).