What does that is mean?
that is
Definition
Introduces the same thing said again in other, usually plainer, words.
Example sentences
Cardiovascular risk, that is, a risk of heart problems.
According to the study, up to four cups a day are not associated with a higher cardiovascular risk, that is, they don't bring more risk to the heart. The magazine, on the other hand, recommends at most two, because of sleep and blood pressure.