  Using a high-resolution cosmological $N$-body simulation, we identify the
ejected population of subhalos, which are halos at redshift $z=0$ but were once
contained in more massive `host' halos at high redshifts. The fraction of the
ejected subhalos in the total halo population of the same mass ranges from 9%
to 4% for halo masses from $\sim 10^{11}$ to $\sim 10^{12}\msun$. Most of the
ejected subhalos are distributed within 4 times the virial radius of their
hosts. These ejected subhalos have distinct velocity distribution around their
hosts in comparison to normal halos. The number of subhalos ejected from a host
of given mass increases with the assembly redshift of the host. Ejected
subhalos in general reside in high-density regions, and have a much higher bias
parameter than normal halos of the same mass. They also have earlier assembly
times, so that they contribute to the assembly bias of dark matter halos seen
in cosmological simulations. However, the assembly bias is {\it not} dominated
by the ejected population, indicating that large-scale environmental effects on
normal halos are the main source for the assembly bias.
