Alfabeto
From Latin alphabetum, from the first two Greek letters alpha (a) and beta (b)
The alfabeto (alphabet) is the complete set of letters of a language, usually shown in a fixed order and used to build the words of that language.
Here is the Spanish alfabeto:
A B C D E F G H I J K L M N Ñ O P Q R S T U V W X Y Z
Notice the extra letter Ñ that English does not have — it sits between N and O.
Note
In 1995, the Real Academia Española (the official authority on Spanish) removed the letters ch and ll from the alphabet. That does not mean the sounds they represent disappeared — it only means that words containing them are now alphabetized under c and l respectively in dictionaries.