Analysis of Variance, the statistical method used to test for differences in means among several treatment groups. In brief, you start with a statistical model, such as y = u + Block + Treat + error. ANOVA then partitions the variation in your Y variable among the explanatory terms on the right side of the equation. From these pieces of variation, an Ftest can be constructed that tests if treatment means are equal, or in statistical language Ho: u1 = u2 = u3 = u4 Ha: at least one mean not equal. SAS Proc Mixed has an abbreviated version of the "ANOVA table", that summarizes the tests performed, as illustrated here. 
The Ftest, along with its two degrees of freedom, produces a significance probability, or Pvalue (Pr>F). If the Pvalue is below your chosen significance level (generally .05), you reject Ho and conclude that at least one of the treatment means differs.
