In some contexts, French uses the definite article where in English you'd use the indefinite (or no) article. This happens with some constructions or verbs but also occurs in some idioms and often used phrases.

Ils marchent comme des danseurs. -- They walk like dancers.
J'aime le chocolat.  -- I like chocolat.
Dans ce film ils font l'amour. -- In this movie they have sex.

Thanks for the response.  I in fact did not tick the box to tell it to send me emails so I did not realise there had been a response, so sorry for delay.

Unfortunately still don't get it.    In your example "J'aime le chocolat" I get.  But still don't get how and why I would choose des for "ils marchent comme des danceurs" .  I guess Les would be specific dancers.  If there is any lesson that explains this and why I would use it I would love to see it.  I have ticked email notifications this time!

In fact I think I have found it:   Plurals of the and a = les and des (articles) in French

The plural forms of le, la and l' is les

The plural forms of un and une is des

Voila!  Simple as that.  I live in France and have been studying French on and off for 20 years have have missed that one.