# What is the difference between two-sided and one-sided fisher exact test?

I am trying to understand the meaning of the null distribution in Fisher Exact Test.

Suppose I have a contigency table:

        Stat1   Stat2
Group1     18       2
Group2      3      40


If I want to know if Stat1 is enriched significantly in Group1, have I to use two-sided test? Is it possible that two-sided test gives me also the probability that Stat1 is enriched in Group2 (another alternative to the null hypothesis)?

The other question might be whether this would be a typical construction of a Fisher's Exact Test. "Two-sided" is the default for R's fisher.test function, but you can specify other alternatives.