Scriptreference explanation

Hi,
Im used to using MVC and just started on an WebForms project, however there is something i just do not understand and been researching it a bit, but maybe someone is able to dumb it down for me.
I see this in the master file:
<asp:ScriptManager runat="server"> <Scripts> <asp:ScriptReference Name="MsAjaxBundle" /> <asp:ScriptReference Name="jquery" /> <asp:ScriptReference Name="bootstrap" /> <asp:ScriptReference Name="respond" /> <asp:ScriptReference Name="WebForms.js" Assembly="System.Web" Path="~/Scripts/WebForms/WebForms.js" /> <asp:ScriptReference Name="WebUIValidation.js" Assembly="System.Web" Path="~/Scripts/WebForms/WebUIValidation.js" /> <asp:ScriptReference Name="MenuStandards.js" Assembly="System.Web" Path="~/Scripts/WebForms/MenuS ...