Hung parliament means that no party has an overall majority of 326 (I think) or more seats, so two parties can form an alliance (coalition) to make it up to or above 326 seats, which means even though Tories may have a small majority, that the SNP and Labour for example could join forces and be a coalition government, as we had with Tory/Lib Dems a few years ago...
But it can mean that 2 parties fighting for different things are in power together.