We're in the midst of a major change sweeping the Web: the familiar HTTP prefix is rapidly being replaced by HTTPS. That extra "S" in an HTTPS URL means your connection is secure and that it's much harder for anyone else to see what you're doing. And on today's Web, everyone wants to see what you're doing.
HTTPS has been around nearly as long as the Web, but it has been primarily used by sites that handle money—your bank's website, shopping carts, social networks, and webmail services like Gmail. But these days Google, Mozilla, the EFF, and others want every website to adopt HTTPS. The push for HTTPS everywhere is about to get a big boost from Mozilla and Google when both companies' Web browsers begin to actively call out sites that still use HTTP.
The plan is for browsers to start labeling HTTP connections as insecure. In other words, instead of the green lock icon that indicates a connection is secure today, there will be a red icon to indicate when a connection is insecure. Eventually secure connections would not be labeled at all, they would be the assumed default.
Google has also been pushing HTTPS connections by "using HTTPS as a ranking signal," meaning Google takes the security of a connection (or lack thereof) into consideration when ranking sites in search results. For the time being, Google says that HTTPS is "a very lightweight signal... carrying less weight than other signals such as high-quality content." However, the company says that it "may decide to strengthen" this indicator as a means to encourage more sites to adopt HTTPS.