What is arrangement specifier(.16b,.8b) in ARM assembly language instructions?

I want to what exactly is arrangement specifier in arm assembly instructions.

I have gone through ARM TRMs and i think if it is size of Neon register that will be used for computation

for e.g. TBL Vd.Ta, {Vn.16B,Vn+1.16B }, Vm.Ta

they mentioned Ta to be arrangement specifier of value 16B or 8B

This is taken from http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0802a/TBL_advsimd_vector.html