Difference between key-value stores and key-value pairs

Difference between key-value stores and key-value pairs or
Difference between  Key-value stores  and document db or
Difference between Redias and mongoDb .
 
Key Values always Confused me that's why i decided to share my some short of experience, In NoSQL Databases KV Pair and KV Stores are different. Event they are related to different database vendors too.

Key-Value stores ; store keys value pairs  in buckets, exactly like a hash table data structure; where each key must be unique.  They are extremely fast for writing, and extremely fast for reading and updating. if you have the key.  They are slow on multiple updates and if you have to query the entire store.  You see Key-value stores used a lot as caching stores because of their fast reads.
eg: Redis, Riak, memcached, Azure's tablestore, etc

Document Stores ; store data in "documents", typically XML or JSON documents. They're typically schema-less, so each document can contain any data that you want them to have and you can change it on the fly. Documents contain key value pairs, which can be any sort of value, array, or even another document.
eg: mongoDb,CouchDB