This means that the party that won the largest number of MPs didn’t secure a big enough majority to form a government that would work. In this situation, the government would constantly need the support of other parties to help it pass laws and this is not likely to happen.
So when this happens, parties start negotiating with each other to see if they’d be able to work together to form a coalition government.
For example, after the UK general election in 2010, the Conservative Party got the most MPs. But its majority was not large enough to form a workable government. The Labour Party had the second largest number of MPs.
The party with the third highest number of MPs, the Liberal Democrats, held talks with both the Conservatives and Labour to see if they could strike a deal with one of them.
The Lib Dems decided to go into government with the Conservatives. This meant that the Conservatives could rely on the Liberal Democrats to support them on important issues and help them to get laws made.
A coalition agreement was signed which meant that the Conservatives promised to drop some policies that the Lib Dems didn’t like and support some policies that the Lib Dems were keen on.