Recently I have been looking for full forms of many terms, and decided to list them here as I look up them online.

SEO spam: Search engine optimization spam. Spam messages that aim to fool search engines and rank higher in web searches.
CSRF (pronounced sea-surf): Cross-site request forgery. The cases where a hidden link in a web page connects to another web page, and carries out interactions without your approval.

PAC proof: probably approximately correct proofs. They were proposed in 1984 by Leslie Valiant

STEM stands for science, technology, engineering, and mathematics

MUVE: multi-user virtual environments

Error 403, hotlinking: Putting an image/video etc.  link to your HTML code that points to another website. For example: <img src=”image.jpg” > is okay, but <img src=”; > is hotlinking. Folks do not like hotlinking, because it is basically stealing the bandwidth.
The SSCCE: Short, Self Contained, Correct (Compilable), Example