What is this[...] in C#?

Question

C++ / C#

String Here is a piece of the class in which it is located

public VkResponse this[object key]

Answer 1

This is the Indexer
https://docs.microsoft.com/en-us/dotnet/csharp/pro...
In terms of meaning, it is a function that returns some VkResponse from key (which is object).
Syntactically, calling an indexer looks like calling by index in an array (with square brackets)

Answer 2

Gets the value by key key, the same dictionary, or in this case json.