arrays - JavaScript syntax issue: [{ }] hierarchy -

i came across following nested array , little confused why uses particular syntax:

var allquestions = [{    question: "which company first implemented javascript language?",    choices: ["microsoft corp.", "  sun microsystems corp.", "netscape communications corp."],    correctanswer: 2 }]; 

full example: http://jsfiddle.net/alxers/v9t4t/

is common practice use [{...}] having declared such variable?

the definition array object literal in it. not realy nested array.

{  question: "which company first implemented javascript language?",  choices: ["microsoft corp.", "  sun microsystems corp.", "netscape communications corp."],  correctanswer: 2 } 

is object literal, array contains. in fiddle linked there several of these defined in allquestions array. doing makes easy loop on array of questions , display each in turn.