Updated description about nil (#1735)

concepts/nil/about.md

@@ -1,6 +1,6 @@
 # About
 
-[Nil][nil-dictionary] is an English word meaning "nothing" or "zero". In Ruby, `nil` is used to express the _absence_ of an object. In other programming languages, `null` or `none` values may play a similar role.
+[Nil][nil-dictionary] is an English word meaning "nothing" or "zero". In Ruby, `nil` is an object which is used to express the _absence_ of a value. In other programming languages, `null` or `none` values may play a similar role.
 
 ```ruby
 # I do not have a favorite color