Hello KarinaH, Besides "idioms" as Mario said very well, they're known as "modismos". Also, at least in Spain, often refer to them as "frases hechas". Spanish is also full of idioms. Here at this link, I put a lot of them of common use in Spain with an example of each one: ☛ http://www.italki.com/question/253491 Hope this helps you, KarinaH. Have a nice day!

"Idioms" in Spanish are "expresiones idiomáticas".

Además de expresiones idiomáticas, en un lenguaje mas coloquial se podría traducir por "expresiones" o "formas de hablar".

Hello. The word idioms in Spanish are phrases that have a figurative meaning. For example, If somebody say in Spanish "Esto fue pan comido" it doesn't mean that somebody ate a piece of bread. It mean that something was very easy.