1) That which nullifies the fast and (as a result) obligates the making up of the fast only:
a) Eating and drinking intentionally;
b) Intentionally vomitting.
The Messenger of Allaah (sal-Allaahu 'alayhe wa sallam) said:
((Whoever intentionally vomits, then he has to make up the fast)),[Saheeh, transmitted by al-Haakim and others];
c) Menses and post-partum bleeding – even if it occurred just moments before sunset;
d) Excreting semen – whether it is as a result of a man kissing his wife, hugging her or masturbating. Then this nullifies the fast and obligates the making up of the fast (of Ramadhaan) for that day.
2) That which nullifies the fast and (as a result) obligates the making up of the fast in addition to paying a penalty.
According to the majority of the scholars this only applies to sexual intercourse. The penalty is either freeing a slave or fasting continuously for 2 months or feeding 60 poor and needy people. Both the men and women are regarded equal in this ruling.