Check out this article to learn what a grantee is. For real estate, a grantee is a person receiving an interest in real estate by a deed.
In the HeirShares Tree Builder, any time a user informs the tree builder that there is a deed, the user will be asked to provide information about what is written in the deed, including listing the names of every person granted an interest in the deed- the grantees.
This image of a deed illustrates in pink where that information would be found in the deed. In this example, there are three grantees, as highlighted by the numbers.