What happens? And what's different in 2020?

Balloons. Dancing. Speeches. Music. It's convention season in the US election, but this year won't be like previous ones.

First, the Democratic National Convention starts with four days of party events leading up to the main event: naming the presidential nominee.

Then the Republican National Convention will follow a similar format, and is due to run from 24 August to 27 August.

But first, what is a convention and how will coronavirus affect this?