HyperText Markup Language: the web page itself, including text and markup tags.
Like nearly all database engines, MySQL accepts commands in Structured Query Language (SQL). SQL is the way that every user (including a PHP program) communicates with MySQL.
Cascading Style Sheets: styling and layout rules applied to the elements in an HTML document.
Probably the most interesting new elements in HTML5 are <audio>, <video>, and <canvas>, although there are many others such as <article>, <summary>, <footer>, and more.
Some of these technologies are controlled by companies that accept bug reports and fix the errors like any software company. But open source software also depends on a community, so your bug report may be handled by any user who understands the code well enough. You may someday fix bugs in an open source tool yourself.