Uncaught ReferenceError: $ is not defined

var map;
$(document).ready(function () {
    InitializeMap();
});


function InitializeMap() {
    var latlng = new google.maps.LatLng(-33.956009, 25.601481);
    var myOptions = {
        zoom: 15,
        center: latlng,
        mapTypeControl: true,
        mapTypeControlOptions: { style: google.maps.MapTypeControlStyle.DROPDOWN_MENU },
        navigationControl: true,
        navigationControlOptions: { style: google.maps.NavigationControlStyle.SMALL },
        mapTypeId: google.maps.MapTypeId.ROADMAP
    };
    map = new google.maps.Map(document.getElementById("map"), myOptions);
}
window.onload = InitializeMap;
var bikeLayer = new google.maps.InfoWindow();
bikeLayer.setMap(map);


var companyPos = new google.maps.LatLng(-33.956009, 25.601481);

var companyMarker = new google.maps.Marker({
    position: companyPos,
    map: map,

    title: "Erica",
    zIndex: 3
});

google.maps.event.addListener(companyMarker, 'click', function () {
    bikeLayer.open(map, companyMarker);
});

"Uncaught ReferenceError: $ is not defined "

$(document).ready(function () {