What does it mean that an hypotesis is consistent?
I'm not especially familiar with this but from the example provided we can deduce that:

An hypothesis is a partial assignment of values to the features. That is, by &quot;applying the hypothesis&quot; we obtain a subset of instances for which the features satisfy the hypothesis.
An hypothesis is consistent with the data if the target variable (called &quot;concept&quot; apparently, here EnjoySport in the example) has the same value for any instance in the subset obtained by applying it.

First case: $h_1=&lt;?,?,?,Strong,?,?&gt;$. All 4 instances in the data satisfy $h_1$, so the subset satisfying $h_1$ is the whole data. However the concept EnjoySport can have two values for this subset, so $h_1$ is not consistent.
Second case: $h_2=&lt;Sunny,Warm,?,Strong,?,?&gt;$. This hypothesis is more precise than $h_1$: the subset of instances which satisfy $h_2$ is $\{1,2,4\}$. The concept EnjoySport always have value Yes for every instance in this subset, so $h_2$ is consistent with the data.
Intuitively, the idea is that an hypothesis is consistent with the data if knowing the values specified by the hypothesis gives a 100% certainty about the value of the target variable.