What is a symbol code?
"Symbol Codes" means codes that work over a (finite) alphabet with an arbitrary size. Many times people focus only on binary codes, and Shannon Thm says that the minimal code length of some random variable $X$ is between $H(X)$ and $H(X)+1$ bits.

But what if, instead of bits, you use trits, or symbols from a larger alphabet of size, say, $a$?  Then, the length of $X$'s coding needs to be adjusted since every symbol of the codeword now "contains"  $\log_2 a$ bits.
Then, the wikipedia page says, the minimal code length will be 
between $H(x)/\log_2(a)$ and $H(x)/\log_2(a)+1$ symbols. 

Multiply the equation by $\log_2 a$ to convert into information bits:
the codeword will have $S$ symbols, hence $S\log_2 a$ bits, and this amount, by Shannon's coding theorem, can be minimized so that it is almost $H(X)$ (maybe up to one additional symbol, i.e., additional $\log_2 a$ bits).