Can some one explain what is the meaning ( in real life) of anti causal (precursor) part of the channel taps?
Actual channels are always causal (like everything else in the physical universe).

Actual (discrete-time) channels also sometimes have one tap that is considerably larger than the rest; an example impulse response would be h = [0.1, 1.5, 0.2]. Some authors prefer to define h[0] as the largest tap; in my example, we'd have h[-1] = 0.1, h[0] = 1.5, and h[1] = 0.2. Then, h[-1] would be "anticausal" since it occurs before the impulse is applied at n = 0.

As Marcus says, this is just a model. It has zero effects on the receiver, except on how you write the indices in your algorithms.

Personally, I never worry about this and always define the first tap as h[0] (or rather h[1], if implementing it in Matlab or Julia).