cal terminal value

when calculate terminal value in a multi-stage valuation model, the formula is as below: what is trailing P/E and leading P/E? Thanks. TVn=(trailing P/E) x (earnings in year n) TVn=(leading P/E) x (forecasted earnings in year n+1)

trailing or leading refer to earnings. trailing P/E = P0/E0 leading P/E = P0/E1