Difference between "click" & "visit" in Google Analytics?

No both are different. Lets take an example like one visitor come to your website that is called visit but when he goes to different internal pages to your website that is clicks.

There is an important distinction between clicks (such as in your AdWords Campaigns reports) and visits (in your Search Engines and Visitors reports report). The clicks column in your reports indicates how many times your advertisements were clicked by visitors, while visits indicates the number of unique sessions initiated by your visitors. There are several reasons why these two numbers may not match:

• A visitor may click your ad multiple times. When one person clicks on one advertisement multiple times in the same session, AdWords will record multiple clicks while Analytics recognizes the separate pageviews as one visit. This is a common behavior among visitors engaging in comparison shopping.

• A user may click on an ad, and then later, during a different session, return directly to the site through a bookmark. The referral information from the original visit will be retained in this case, so the one click will result in multiple visits.

• A visitor may click on your advertisement, but prevent the page from fully loading by navigating to another page or by pressing their browser's Stop button. In this case, the Analytics tracking code is unable to execute and send tracking data to the Google servers. However, AdWords will still register a click.

• To ensure more accurate billing, Google AdWords automatically filters invalid clicks from your reports. However, Analytics reports these clicks as visits to your website in order to show the complete set of traffic data.

Visit: User or visitor browse your site and view things. More visitor is called as traffic.
Click: Visitor click on Ad display on you site through which you earn.

Visit is just an impression, a click is the user taking action on your site and putting money in your pocket.