The buried via is the hole made between inner layers used to interconnect the inner layer signal. It can not be visible from surface layers of top and bottom layer. Generally, they're often used on the mobile phone,PDA board etc.
A) Reduce the probability of signal interference;
B) Keep the continuity of the characteristic impedance of the transmission line;
C) Save wiring space, suitable for high density and high speed circuit board design;
Mobile phone, PDA boards, telecommunications, complext modules.