Core - Open ended funds that invest in properties with stabilized cash flow and have historically employed leverage in the 20% range.
Value added - Closed end funds that invest in properties that have uncertainty in their cash flow (low occupancy and requires some capex) and have historically used leverage in the 50% range.
Opportunistic - Closed end funds that invest in properties that have the most uncertainty in their cash flows (development, empty buildings) that have historically used leverage in the 60% range.

These are the hard and fast rules. Joe's initial paper provides some more insight.

https://faculty.chicagobooth.edu/-/media/faculty/joseph-pagliari/docs/r…