php - What is the meaning of []

I have a code as below and I am not sure what type of data
variable $ACTIVITYGROUPS[] has and how do I read it
?

$ACTIVITYGROUPS[] =
            saprfc_table_read ($fce, "ACTIVITYGROUPS",
            $i);

When I did
print_r(saprfc_table_read ($fce, "ACTIVITYGROUPS", $i); I got
bunch of arrays without any seperator and not sure how to exactract the data. can
someone tell me what does it do in above sentences
?

Here is what
print_r(saprfc_table_read ($fce, "ACTIVITYGROUPS", $i); result
gives me:

Array (

            [AGR_NAME] => Y:SECURITY_DISPLAY
 [FROM_DAT] => 20080813

            [TO_DAT] => 99991231
 [AGR_TEXT] => Security Display - Users &
            Roles
 [ORG_FLAG] => C
)


Array
            (
 [AGR_NAME] => Y:SECURITY_ADMIN_COMMON
 [FROM_DAT] =>
            20080813
 [TO_DAT] => 99991231
 [AGR_TEXT] => Security
            Administrator
 [ORG_FLAG] => C
)

Array
            (

 [AGR_NAME] => Y:LOCAL_TRANSPORT
 [FROM_DAT] =>
            20090810
 [TO_DAT] => 99991231
 [AGR_TEXT] => Transport into
            target client - DEV system only
 [ORG_FLAG]
            =>
)