I am not too sure what abbreviations you are asking about, but here are some of the most basics. Have any specifics in mind?
SEO = Search Engine Optimization/Optimisation (US/UK) / Optimizer
HTML = HyperText Markup Language
PHP = Hypertext Preprocessor
SQL = Structured Query Language
URL = Uniform Resource Locator
CSS = Cascading Style Sheets
WWW = World Wide Web
.com - Stands for company/commercial, but it can pretty much be used for any web site.
.net - Stands for network and is usually used for a network of sites.
.org - Stands for organization and is supposed to be for non-profit entities.
.us, .nu, .co.uk, - Are country specific domain extensions that may require the register to be a citizen of the given country.
.biz, .info - These and other like them are domain types that have been added because there are barely any short and intelligible domain addresses left to register.