The word “mate” is often an unknown for many Spanish people. The reason for this is that it is generally used verbally rather than in the written form and, in addition to that, it is a colloquial expression.
The students that I know that use it tend to have gone to the UK or Australia for a year or so. The meaning of the word “mate” is “friend”. So you can say: “I have got a lot of mates in London” or “Do you know where the train station is, mate?”
The second example is a good one because it shows how the expression is often used and it is especially strange because it is often used even in the context where you are speaking to someone who is NOT your friend or complete stranger! I know....a little weird! Some of my Spanish students say that it is similar to the word “tio” in Spanish.
Hope that helps!
Soy el director de Daniel Smith + Partners. Tengo más de 10 años de experiencia enseñando inglés a españoles.