Nigel Farage is (was) the MP (Member of Parliament) for the Clacton area. He is currently under investigation by the parliament's standards watchdog after reports that he failed to declare some donations and benefits.
If he’s found to have broken the rules, it’s possible he’d be suspended from parliament and subject to a recall election. However, he has resigned from this position himself instead, which means there will be a by-election for that seat.
It’s widely perceived that he has done this to distract from the investigation, with the view being that if he runs, then wins, a parliamentary suspension looks like a coordinated attack on someone who has just proven he has local support.
The major UK parties have decided not to field candidates in this election, claiming it is a distraction tactic and a waste of resources. This will leave Farage campaigning head-to-head with a man dressed as a bin, neutering any claims that this is a “real” election win (as well as generating plenty of entertaining news footage over the next few weeks).