It means the plant has flowered when it is not supposed to, as in: Cabbage bolting into flower (usually in the second year)

Would that be the reason why pansies have a tendency to bolt, Vincent (I'm assuming your name's Vincent, excuse me if I'm wrong)? I've often wondered what causes them to get long and straggly.

The pansy that we grow as bedding is really a perennial but has been bred for large flowers in the first year. So in the second year they don't really 'bolt', it is just that their breeding means they excel in the first year and then become straggly in the second. A bit like a horse that is bred to run a mile but not a mile and half!!
Vincent

Oh right. Does that mean that the pansies that were bought this year but that have become leggy are actually last year's plants?

Not necessarily, they may have just been grown 'soft' as in a greenhouse or or shade or whatever. You can cut them back and they will resprout but usually not worth the trouble.

Thanks. They're in mixed baskets so I might just cut them back and see what happens. They can't look worse than they do now.