Originally posted on 03/22/2013:

It means OVER 5.75.

In case of 5 goals, you lose your bet.
In case of 7+ goals, you win your bet.
In case of 6 goals, you win 1/2 of your bet.

Let's say you risked 100$ on Over 5.75 (also known as Over 5.5&6) at +100 odds. (2,00 Decimal)

If game ends 4-2, return is 150$ so your net profit is 50$.