What is the difference between the strings and the words of a language?

A string is any combination of the letters of an alphabet where as the words of a language are the strings that are always made according to certain rules used to define that language.For example if we take Alphabet Σ = { a , b }  Here a , b are the letters of this alphabet.
As you can see we can make a lot of strings from these letters a and b.
For example   a,b,aa,ab,ba,bb,aaa,aab,aba,baa,…………………………………………………… and so on.
But when we define a language over this alphabet having no a’s and only odd number of b’s. Then the words of this language would have only those strings that have only odd number of b’s and no a’s.some example words of our defined language are b , bbb , bbbbb , bbbbbbb ,……………………………..and so on.
So we can say that all the words are strings but all the strings may not be the words of a language.Hence strings are any combination of letters of an alphabet and the words of a language are strings made according to some rule.