What is the difference between a steppe and a prairie?

A steppe is a plain with no trees (except perhaps around waterbodies). It is similar to a prairie. The difference is that prairies tend to have long grass species whilst steppes often have short grass species. However, prairies are also considered one type of steppe.

So the differences are not absolute!

Whilst the word steppe often conjures up the vast plains of Russia, sub-tropical steppes are also found in parts of Greece, Australia and Spain (and many other places)

http://www.ecst.csuchico.edu/~ranger/samples/APCG360/Fall2007/Spiderwebs_Design/learning/ecosystems/pands.html

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