What's an option?

Scuse the stupid question but Aaron mentioned some writers here have had scripts optioned. Is an option where a producer says, "I like the script, let me try and sell it / place it for you"? Or is an option where money has changed hands and its a firm deal?

It means they have the option to develop your script further. Developing a script for a feature film can take years with loads of rewrites so they pay you to develop it. You can't show it to anyone else while it's under option but there's no guarantee it will get produced

That's a name i recognise, Mystergeneral, how are you? (old STW name)
So an option in sitcom doesn't necessarily involve cash, just the promise of 'first dibs'? Sorry for being so thick.

It does mean first dibs, but normally comes with a nominal fee.

I've had a producer say, "I like the script, let me try and sell it/ place it for you" But no option as of yet. As I understand it, they pay you a small amount of money and that means you can't take the project elsewhere for 12 months (or maybe the time period differs from company to company?) but I'm pretty sure that they can't hold on to it for years as they do in the film business.