Román paladino

[poli]

I think it mean in simple Spanish, but I am not sure.

[Don José]

Yes. History and example:
http://desequilibros.blogspot.com.es/2007/09/en-romn-paladino.html#.T6fZT2b0EYw

[poli]

Thank you.
In case you don't know, in English the equivalent term is plain English.

[aleCcowaN]

In spite of its origin -or owing to it- it's now an idiom meaning "popular language easy to understand":

-¿De qué murió?
-Por un aneurisma de aorta abdominal.
-¿En román paladino? (en fácil; en cristiano; etc.)
-Se le desgarró una arteria del vientre.

[Rusty]

To say the same thing in English, here are some options:

In plain English
In English, please
In layman's terms
In English, this time
Say what?!?

[aleCcowaN]

In layman's terms :approx: en términos legos

If asked, "en términos legos" calls to avoid jargon; "en román paladino" calls to avoid sophisticated learned words. Both can be used calling to avoid technicalities.