What does "true mean is not equal to 0" mean in R? I'm doing test for set a data and a statement appears

true mean is not equal to 0

What does it mean?
t.test(Spread.sheet.VNV.Height$Height..CM.2,conf.level = .90)

    One Sample t-test

data:  Spread.sheet.VNV.Height$Height..CM.2
t = 11.648, df = 31, p-value = 7.432e-13
alternative hypothesis: true mean is not equal to 0
90 percent confidence interval:
 18.87785 25.30965
sample estimates:
mean of x 
 22.09375 


You need to read the entire line, since it specifies that it is telling you the alternative hypothesis for the test:

alternative hypothesis: true mean is not equal to 0

In a one sample T-test you have a specified value for the true mean under the null hypothesis.  In the present case your null hypothesis is that the true mean is zero and the alternative hypothesis is that it is not zero.  (Note that the null value is set using the mu value in the t.test function; by default this is set to zero.)
