The $() factory function: in JQuery

All type of selectors available in jQuery, always start with the dollar sign and parentheses: $().

The factory function $() makes use of following three building blocks while selecting elements in a given document:

jQuery	Description
Tag Name:	Represents a tag name available in the DOM. For example $('p')selects all paragraphs in the document.
Tag ID:	Represents a tag available with the given ID in the DOM. For example$('#some-id') selects the single element in the document that has an ID of some-id.
Tag Class:	Represents a tag available with the given class in the DOM. For example $('.some-class') selects all elements in the document that have a class of some-class.

All the above items can be used either on their own or in combination with other selectors. All the jQuery selectors are based on the same principle except some tweaking.

NOTE: The factory function $() is a synonym of jQuery() function. So in case you are using any other JavaScript library where $ sign is conflicting with some thing else then you can replace $sign by jQuery name and you can use function jQuery() instead of $().