The majority voted against an amendment introduced by Opposition Leader Bill Shorten, which means it was unsuccessful.
What was the amendment?
The House was being asked to vote on the bill's main idea (that is, they were voting on whether to give the bill a second reading). The main idea of the bill is to make it possible for the government to hold a national plebiscite to ask Australians "Should the law be changed to allow same-sex couples to marry?"
Shorten's amendment would have changed that question of whether to agree to the bill's main idea so that the House would instead be asked whether they agreed that
this bill be withdrawn and redrafted to legislate for marriage equality and that the House calls on the Government to afford all members of parliament a free vote
What does this amendment mean?
Shorten was against holding a same sex marriage plebiscite and instead wanted to have a free vote in the House on the question of whether to allow same sex marriage.
What is a free vote?
The Parliamentary Education Office explains that a free vote (or conscience vote):
means that members of parliament are not obliged to vote with their party; instead, they can vote according to their own beliefs ... Each parliamentary party decides if its members are allowed a conscience vote on a particular issue.
A conscience vote may be held in order to prevent members of parliament crossing the floor [or 'rebelling'] on a controversial issue which may otherwise cause embarrassment to the team, or to allow members of parliament to express their own strongly-held beliefs.
What is a national plebiscite?
The bills digest explains that:
a national plebiscite is a vote by citizens on any subject of national significance but which does not affect the Constitution. Plebiscites are normally advisory and do not compel a government to act on the outcome. There have only been three national plebiscites—two on conscription during World War I (both defeated) and one on the choice of a National Song in 1977.
Why don't some supporters of marriage equality support this bill?
Several parties and independents oppose this bill for two main reasons: cost and concern that a plebiscite could harm members of the LGBTI community.