The fertile window refers to the period of time when a woman is most likely to get pregnant if she engages in intercourse. The fertile window for most women is about 6 days long.
On average, it includes the five days prior to ovulation and the day of ovulation. That said, the highest chance of conception occurs when intercourse happens 1-2 days prior to ovulation, and you should do your best to have intercourse at that time if you are trying to get pregnant. This is because the sperm take several days to travel up the reproductive tract to the fallopian tube, where they meet and fertilize the egg. Hence, if you have sex after ovulation, the sperm will not reach the egg in time to fertilize it and you will not get pregnant.