https://medium.com/@verdi/hash-tables-aa7e5b4933c3

Hash tables utilize key-value pairs to store data. Because of their speed and utility almost every programming language ships with some type of hash table implementation. Hash tables in Javascript are called Objects, in Python its Dictionaries and in Java, Go and Scala its Maps. Hash tables came to exist because humans think in more than just numbers.

Arrays are great, but having to model all of your data based off indices is a nightmare. So, hash tables exist because being able to model your data like this passwords["gmail"] is way better than having to model it like this passwords[0].