N-COUNT
前置代碼（置于一組號碼前的數字或字母，表示所屬區域等）
A prefix is one or more numbers or letters added to the beginning of a code number to indicate, for example, what area something belongs to.
例句
To telephone from the US use the prefix 011 33 before the numbers given here...
如果從美國打電話，就要在所給號碼前加撥011 33。
I soon learnt to read the licence plates' prefixes.
我很快就學會了識別牌照前面的代碼。