This is defined as a station movement from a bss in one ess to a bss within another ess. this case is supported only in the sense that the station can move. maintenance of upper-layer connections supported by 802.11 cannot be guaranteed. in fact, disruption of service is likely to occur. select one:
a. no transition.
b. bss transition
c. iss transition
d. ess transition

d.

Explanation:

With my experience in the field of information technology, it seems that the term being defined is ESS transition. This is basically (like mentioned in the question) a station movement from a BSS in one ESS to a BSS in another ESS. An ESS is an extended service set which describes one or various different interconnected basic service sets (BSS) as well as the LAN's that they are associated with.