Multidimensional array has more than 1 dimension, such as 2 dimensional array, 3 dimensional array etc.
Define a dimensional array once at initialization.
var arr = [ [2,4], [20,40], [200,400] ]; arr[1][1]; //40
Define a dimensional array dynamically.
var arr= new Array(); arr[0] = new Array(); arr[0][0] = 1; arr[0][1] = 2; arr[1] = new Array(); arr[1][0] = 3; arr[1][1] = 4; arr[1][0]; //3
Define a dimensional associative array dynamically.
var efs = new Array(); efs["em"]=new Array(); efs["em"]["em"] = 1; efs["em"]["g5"] = 1899.10078; efs["em"]["xy"] = 1000; efs["em"]["d5"] = 1; efs["g5"]=new Array(); efs["g5"]["em"]=0.0005; efs["g5"]["g5"]=1; efs["g5"]["xy"]=0.5265; efs["g5"]["d5"]=0.0005265; efs["em"]["xy"]; //1000