jQuery is needed for the following list:-
Efficiency of web page increases when minimized version of jQuery is used.min.js file will be more than 50% less than the normal js file. Reduction in the file size makes the web page faster.
Dollar Sign is nothing but it's an alias for JQuery.
jQuery no-conflict is an option given by jQuery to overcome the conflicts between the different js frameworks or libraries. When we use jQuery no-conflict mode, we are replacing the $ to a new variable and assigning to jQuery some other JavaScript libraries. Also use the $ (Which is the default reference of jQuery) as a function or variable name what jQuery has. And in our development life, we are not at all strict to only jQuery.
$(document).ready() function is the starting point of jQuery code. It is executed when DOM is loaded.
: jQuery filter is used to filter the certain values from the object. It filters the result of your original query into specific elements.
JavaScript famous keyword this always refers to the current context.
A callback is a plain JavaScript function passed to some method as an argument or option. Some callbacks are just events, called to give the user a chance to react when a certain state is triggered.