There is both polymeter and polyrhythm.


  Polymeter is sometimes referred to as "tactus-preserving polymeter." The measure size differs, the beat is the same. Since the beat is the same, the various meters eventually agree.


https://en.wikipedia.org/wiki/Meter_%28music%29#Polymeter

A good example of polymeter is the Tala which is an extream form of complex time.


  Polyrhythm is the simultaneous use of two or more conflicting rhythms, that are not readily perceived as deriving from one another, or as simple manifestations of the same meter. The rhythmic conflict may be the basis of an entire piece of music (cross-rhythm), or a momentary disruption. Polyrhythms can be distinguished from irrational rhythms, which can occur within the context of a single part; polyrhythms require at least two rhythms to be played concurrently, one of which is typically an irrational rhythm.


https://en.wikipedia.org/wiki/Polyrhythm

Commonly used in modren Jazz.  See: Mongo Santamaria and Elvin Jones.

What is it called when a music has two concurrent tempos
I'm going on my honeymoon to Thailand, Cambodia and Vietnam in June for 4 weeks.

I'll bring my Canon t3i + 15-55mm and a 55-250mm lens.

This will be my first travel like this and I definitely want to take some awesome pictures.

I don't have a Flash and I want to buy a Canon Speedlite 430EX when the time comes.

The question is... Is it Worth it to buy this flash for this kind of travel?
