JPG: In computing, JPEG (pronounced JAY-peg; IPA: /?d?e?p??/) is a commonly used method of compression for photographic images. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10 to 1 compression with little perceivable loss in image quality. We use JPGs for photos (think images with shading and gradients).
META TAG: Meta elements are HTML or XHTML elements used to provide structured metadata about a web page. Such elements must be placed as tags in the head section of an HTML or XHTML document. Meta elements can be used to specify page description, keywords and any other metadata not provided through the other head elements and attributes. These elements are part of your SEO and online marketing arsenal.
PLATFORM: In computing, a platform describes some sort of hardware architecture or software framework (including application frameworks), that allows software to run. Typical platforms include a computer's architecture, operating system, programming languages and related runtime libraries or graphical user interface. The big two that we test on are Mac and Win!
Last set of terms coming next week - let us know if there are any others you have questions about!