What is the difference between DC base current and signal current in CE transistor amplifier?
If the total base current is denoted with \$i_B(t)\$, and if the time average value (DC value) of \$i_B(t)\$ is denoted with \$I_B\$, then denote the AC (signal) base current as

$$i_b(t) = i_B(t) - I_B$$

and the sentence you came across can be written as "if \$I_B\$ has to be about \$10\cdot i_b(t)\$..."