Gridcell (role) is an element within the table or tree structure. As explained in the grid (role), gridcells will form a relation with their nearest possible parent element. In the table example the gridcells are owned by <tr> or row (role) to form a parent child relation. A gridcell can be focusable with the keyboard, can be editable and selectable.
Use aria-selected (state) to inform the user about the selected or non selected state of the grid cell. If the gridcell is non editable also use aria-readonly (property) to intimate the same to a screen reader user. In a tree structure if the gridcell is having the expand collapse functionality use aria-expanded )state) to intimate the same to the screen reader user.